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THE CHEMISTRY OF PIGMENTS 



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THE 



CHEMISTRY OF PIGMENTS 



BY 



BBNEST J. PAREy, B.Sc. (Lond.), F.I.C, F.C.S, 

AUTHOR OP ** TUB CHBMISTRT OF ESSENTIAL OII£ AND AROlFIOIAIi 



** 



PRRPUMBS, ' BTO. 



AND 



JOHN H. COSTE, F.I.C, RC.S. 



WITH FIVE ILLUSTRATIONS 




OF THE 

UNIVERSITY 

OF 



LONDON 

SCOTT, GEEENWOOD & CO. 

19 LUDGATE HILL, E.G. 

1902 

[All rights reserved] 



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PEEFACE. 

The authors have in the following pages endeavoured 
to indicate the chemical relationships, composition 
and properties of most of the better-known pigments. 
During recent years they have given a great deal 
of attention to the examination of painters' colours, 
and have from time to time found some difficulty 
in obtaining reliable information on the subject. 
This led to a considerable amount of work in 
obtaining and examining specimens of pigments, 
and it was felt that the information thus gained 
might usefully be published. 

Speaking generally, the plan of the authors has 
been to treat the various pigments in groups, aUied 
chemically rather than chromatically. Motives of 
convenience have in some cases led to a modifica- 
tion of this scheme. The methods of manufacture 
of colours have been considered rather from the 
chemical than the technical point of view ; it is 
not suggested by the authors that the present work 
is in any sense a manual of colour-making. 

Analytical processes which, in most cases, the 
authors have by experience found suitable are 
described, and the nature of probable impurities, 



104628 



VI PREFACE. 

adulterations and other causes of inferiority pointed 
out, and numerous analyses of genuine and sophisti- 
cated pigments, for the most part by the authors, 
are given as illustrating the composition of these 
bodies. Preliminary chapters on colour and on the^ 
application of pigments have been added. 

It is the hope of the authors that this work 
may be found of use by those who are called 
upon to use or examine pigments as a guide to- 
the selection of those which are suitable, and the 
rejection of those which as a class or through 
individual inferiority are unsuitable for the class, 
of work to be undertaken. 

K J. P. 
J. H. C 

London, October, 1901. 



CONTENTS. 

CHAPTER I: 

Introductory. 

Light — White Light — The Spectrum — The Invisible Spectrum — 
Normal Spectrum — Simple Nature of Pure Spectral Colour — 
The Recomposition of White Light— Primary and Comple- 
mentary Colours— Coloured Bodies — Absorption Spectra 

pages 1 to 17 

CHAPTER II. 

The Application of Pigments. 

Uses of Pigments: Artistic, Decorative, Protective— Methods of 
Applicatidsn of Pigments: Pastels and Crayons, Water Colour, 
Tempera Painting, Fresco, Encaustic Painting, Oil-Colour 
Painting, Keramic Art, Enamfel, Stained and Painted Glass, 
Mosaic pages 18 to 76 

CHAPTER III. 

Inorganic Pigments. 

White Lead — Zinc White— Enamel White— Whitening — Red Lead — 
Litharge — Vermilion — Royal Scarlet — The Chromium Greens — 
Chromates of Lead, Zinc, Silver and Mercury — Brunswick 
Green- The Ochres — Indian Red — Venetian Red — Siennas and 
Umbers — Light Red — Cappagh Brown — Red Oxides — Mars 
Colours — Terre Verte — Prussian Brown — Cobalt Colours — 
Cceruleum — Smalt — Copper Pigments — Malachite — Bremen 
Green — Scheele*s Green — Emerald Greeny— Verdigris — Bruns- 
wick Green — Non-arsenical Greens — Copper Blues — Ultramarine 
— Carbon Pigments — Ivory Black— Lamp Black — Bistre— Naples 
Yellow — Arsenic Sulphides: Orpiment, Realgar — Cadmium 
Yellow — Vandyck Brown pages 77 to 181 



VUl CONTENTS. 

CHAPTER IV. 

Organic Pigments. 

Prussian Blue— Natural Lakes — Cochineal — Carmine — Crimson — 
Lac Dye — Scarlet — Madder — Alizari n — Cam peachy — Quercitron 
Rhamnus — Brazil Wood— Alkanet — Santal Wood — Archil — 
Coal-tar Lakes — Red Lakes— Alizarin Compounds — Orange and 
Yellow Lakes — Green and Blue Lakes— Indigo — Dragon's 
Blood — Gamboge — Sepia— Indian Yellow, Purree — Bitumen,^ 
Asphaltum, Mummy pages 182 to 275 

Index pages 277 to 280 






THE CHEMISTEY OF PIGMENTS. 



CHAPTEE I. 

INTRODUCTORY. 

Colour phenomena may, broadly, be divided into two classes. 
In the larger and more important group they are due to the 
selective action of what we .know as coloured bodies upon 
light, whilst in the smaller group they are dependent upon 
quite other causes, which, from the point of view of the 
present work, need not be touched upon. The colour effects 
produced by pigments belong entirely to the former class, 
and to intelligently understand the principles of colouring 
materials, an elementary but exact knowledge of the theories 
of light is necessary. In the present chapter the theoretical 
aspect of the subject is briefly referred to from this point of 
view, but no mathematical details are introduced, except 
where absolutely necessary for the comprehension of the 
point at issue. 

Light. 

Light is due to a series of intensely rapid vibrations of 

a medium which is assumed to be imponderable, and to 

pervade all space and matter. Such a medium is, of course, 

physically quite incomprehensible, but its existence must be 

assumed to satisfactorily explain the ordinary phenomena of 

light. These vibrations are transverse, that is, in planes at 

right angles to the direction of propagation of the beam. 

The vibrations in sound waves are, on the other hand, 

1 



2 CHEMISTRY OF PIGMENTS. 

longitudinal, that is, in the direction of the propagation of 
the wave. This hypothesis is known as the wave theory, or 
the undulatory theory of light, the vibrations evidently par- 
taking of the nature of waves. Indeed they may be well 
illustrated by ordinary waves, and the distance between two 
successive crests is termed the wave length, whilst the distance 
from crest to trough is the amplitude. The intensity of the 
wave depends on the latter, whilst its specific character, as 
will be seen later, depends essentially on the wave length. 

White Light. 

The ordinary light of the sun, which we recognise as 
white light, is a mixture of innumerable vibrations of different 
wave lengths, or, what amounts to the same thing, of different 
colours. This is best illustrated by the classic experiment 
of Newton, which was undertaken by him to prove the pro- 
position that ** the light of the sun consists of rays differently 
refrangible" (Newton, Opticks, book i., prop, ii., theorem 2). 
This experiment may be briefly described as follows : Into 
a perfectly dark room (see Fig. 1) a beam of light is ad- 
mitted through a small round hole, 0, and in its path is 
placed a triangular glass prism P. The light falling on the 
prism is refracted or bent (as is always the case when light 
passes from any medium to any other of different density), 
and on being received on the screen Q it is seen that instead 
of a white spot we have an elongated band of different 
colours. This is the " spectrum " S. 

The Spectrum. 

This coloured band, which is called the prismatic spectrum, 
m order to distinguish it from that produced in another man- 
ner {vide infra), is composed of a series of colours, situated in 
the same order as are those in the rainbow, which owes its 



INTRODUCTORX. O 

existence to an action of this kind. As a matter of fact, every 
vibration of different wave length is refracted to a different 
degree, the rays of shorter being more refracted than those of 
longer wave length. Hence the fact that the colours in the 
spectrum merge gradually into one another, and although 
each separate poaition as we advance from one end to the 
other is of a different colour absolutely, we cannot, with the 
eye, enjoy such fine distinctions, so that we are compelled to 
separate the spectrum into arbitrary divisions in which the 



main colour is represented in its various shades. For con- 
venience Newton divided the spectrum into seven parts, 
starting from the least refracted rays, as follows : Eed, 
orange, yellow, green, blue, indigo and violet. Any other 
similar division is quite legitimate — such, for example, as 
the more extended — red, orange red, orange, orange yellow, 
yellow, etc., etc. To exactly define the spectral colours, as 
they are called, however, we need something more exact. 
We have this in the Frauenhofer linea (so named from their 
discoverer), a series of fine dark linea which break the con- 



4 CHEMISTBT OF PIGMENTS. 

tinuity of the spectrum of sunlight. As these dark lines 
depend on the existence of definite elements in the sun's 
atmosphere their position is absolutely fixed, and their posi- 
tions having been determined with accuracy, they can be 
used as points of reference. The most prominent lines are 
those named from A to H, starting from the red end of the 
spectrum. These lines are reproduced as bright lines in the 
same position, when, for example, the element responsible 
for the given line is volatilised in a colourless flame. The 
D Une (which is in reality two lines extremely close together), 
for example, is characteristic of the element sodium. If the 
visible portion of the prismatic spectrum, that is, from the 
red to the violet, be divided into 1,000 parts, the positions of 
these lines are as follows : — 



A 





E 


36311 


B 


74-02 


F 


493-22 





112-71 


G 


763-58 


D 


220-31 


H . 


1,000 



The Invisible Spectrum. 

Hitherto we have referred only to the visible spectrum, 
that is, the coloured bands which are produced when white 
light is decomposed by, for example, a glass prism. But it 
has been shown beyond doubt that heat waves are subject to 
many of the same laws as light waves, and it appears that 
the same class of vibration is responsible for the phenomena 
of heat and light. If a delicate thermometer be placed in the 
various parts of the visible spectrum, it will be found that, if 
we use a prism of, for example, rock salt, which absorbs 
practically none of the vibrations, the temperature varies 
with the portion of the spectrum in which the thermometer 
is placed. The maximum is obtained in the extreme red of 
the spectrum, and a gradual fall occurs till the extreme violet 
is reached. But if the thermometer be moved out of the 



INTRODUCTORY. 5 

spectrum past the red an increase of temperature is noticed, 
a maximum being obtained just beyond the visible rays. 
These invisible rays, which are less refracted, and of greater 
wave length than the visible rays, are the dark heat rays. 
Beyond the violet is also another set of rays which are 
very highly refracted and of very small wave length, which 
are known as the ultra-violet or chemical rays. These 
are closely connected with many chemical effects and with 
fluorescence phenomena, and can, to a small extent, be ren- 
dered visible by special appliances. The spectrum, including 
the ultra-violet and ultra-red rays, may thus be divided into 
chemical, light, and heat rays. 

The phenomena observed in heating a piece of iron will 
illustrate this matter. At comparatively low temperatures 
the slow vibrations in the mass are responsible for the emis- 
sion of the longer or dark heat waves. As the temperature 
increases and the vibrations become more energetic, waves 
of shorter period are emitted, and at length the red of the 
spectrum appears and the iron mass assumes a dull red heat. 
As the temperature becomes more and more elevated the 
vibrations of shorter and shorter period appear and are added 
to the red, and finally all the colours of the visible spectrum 
are emitted, and the iron assumes a white heat. 

The Normal Spectrum. 

Usually, spectra produced by means of a glass prism suffer 
from two defects. Firstly, they are not quite pure, that is, 
the colours seen overlap to a small extent, and therefore the 
continuity of the pure colours is destroyed. Secondly, the 
position of each colour is not exactly in proportion to its 
wavelength, and there is what may be called ''crowding'* 
in places. With very special appliances these defects may 
be almost entirely rectified, however, but by means of a 
diffraction grating we can produce a spectrum that is both 



6 CHEMISTKY OF PIGMENTS. 

pure and normal. A diffraction grating is a system of very 
narrow, equal and equidistant rectangular apertures, usually 
employed in the form of a glass plate with an enormous 
number of parallel fine lines traced on it at equal distances 
with a diamond point, the two series being at right angles to 
each other. When a luminous centre is viewed through this, 
a central or direct image is seen, and on either side of it are 
several spectral fringes richly coloured with all the rainbow 
colours. For the theoretical considerations connected with 
the production of these diffraction spectra, the reader is re- 
ferred to advanced text-books on optics. It here sufiices to 
say that there is no overlapping of the colours, and whilst 
the intensity of the spectrum is small, it has the advantage 
of being quite pure ; and, further, if the diffracted light is at 
right angles to the surface of the grating the spectrum is 
normal, that is, the position of each ray is in exact proportion 
to its wave length. The importance of this is seen by the fact, 
that not only, as mentioned above, is there some overlapping 
in ordinary prismatic spectra, but the irrationality of dispersion, 
as it is called, is so great in some substances that the order 
of the colours is actually reversed. The relative space oc- 
cupied by the various colours in a prismatic spectrum depends 
on the prism, but for ordinary glass prisms made of crown 
glass the following may be taken as representing the relative 
spaces. Those of the normal spectrum are given as well. 
In each case the spectrum is assumed to be divided into 
1,000 parts :— 





Prismatic Spectrum. 


Normal 


Spectrum 


Red 





150 


0- 


- 330 


Orange-red 


150 


195 


330- 


- 435 


Orange . 


195 


210 


435- 


- 460 


Orange-yellow 


210 


230 


460- 


- 485 


Yellow . 


230 


240 


485- 


- 500 


Green-yellow . 


240 


345 


500- 


- 575 


Green 


345 


450 


575- 


- 690 


Blue 


450 


805 


690- 


- 880 


Violet . 


805 — 


1,000 


880- 


-1,000 



IW 



INTRODUCTORY. 7 

The Simple Nature of the Pure Spectral Colours. 

The true spectral colours are of a simple nature, that is, 
they cannot be further decomposed into other colours as 
white light can. This can be shown with great ease in the 
following manner. A narrow slit, A', is made in a shutter 
parallel to an opening, A, in the screen, S, which can be 
moved as desired. The beam of light passing through A is 
allowed to pass through a lens to render the emergent rays 
parallel, and to fall on a prism, P. The spectrum appears 
on the screen, and any desired portion can be made to pass 
through the slit, A, and to again fall on a prism, Q, and after 




Fig. 2. 



traversing this on to the screen, T. It will be seen that the 
image on T is always identical with the light which is allowed 
to pass through the slit A ; hence the light cannot be further 
decomposed. 

The Recomposltion of White Light. 

The above experiments are of an Emalytical nature, but 
the reverse experiments are easy to perform, and white light 
can thus be synthesised from its components. There are 
several methods of effecting this synthesis, amongst which 
the following may be mentioned. A beam of white light 



8 CHEMISTBY OF PIGMENTS. 

may be passed through a prism and so decomposed into its 
component coloured rays, which are then allowed to fall on 
a prism of the same nature in the reverse position, when 
the refraction in the reverse direction takes place, and the 
emergent beam is white again. 

A second, but rough-and-ready method of showing this 
effect is to paint a circle of cardboard in sections with the 
seven principal spectral colours, and rotate it rapidly round 
an axis passing through its centre. Owing to the phenomenon 
of the persistence of vision, the impressions of the colours are 
more or less superimposed, and an approximation to white 
is the actual colour observed. 

Primary and Compiementary Coiours. 

The popular idea that the colours red, yellow and blue 
are " primary " colours on account of the fact that no human 
eye has been able to detect in them two different colours, 
whilst all other colours contain at least two primary colours, 
is quite erroneous, and is based on visible results obtained 
in the mixture of pigments and the transmission of light 
through coloured glasses. The interpretation of these pheno- 
mena is of a different nature, and it is more correct to regard 
each of the spectral colours as primary and elementary. It 
is true that the theory first propounded by Dr. Thomas 
Young, that there are three primary colour sensations, has 
received universal acceptation. This theory propounds that 
there are three chief elements in colour sensations, that is, 
three distinct physiological actions, which, by their various 
combinations produce all our sensations of colour. Each of 
these primary colour sensations is excited by wave lengths 
covering a wide range, but possesses its maximum excita- 
bility for rays of definite wave length. These points of 
maximum sensibility are in the green near Frauenhofer's line 



INTRODUCTORY. 9 

by in the extreme red, and in the extreme violet. The im- 
pression of white light on the retina of the eye may be pro- 
duced by various combinations ; the results are identical 
to the eye, but the differences in the combinations are at 
once perceived when the light is spectroscopically analysed. 
Thus the following pairs of colours, when combined, give 
white light : — 

Red Blue-green. 

Orange Blue. 

Yellow Violet-blue. 

Greenish-yellow .... Violet. 

Green Pink (red-violet). 

Each of the spectral colours which in combination with 
another colour yields white light is said to be complementary 
to that colour; thus yellow and blue are complementary 
colours, and green and red (within the limits as shown above) 
also. The term secondary colour is applied to the colour 
resulting from the mixture of two primary colours, such as 
red and blue, which produce a violet or purple, and tertiary 
colours are those which result from the mixture of two 
secondary colours. These terms, however, are exceedingly 
arbitrary and, consequently, not very scientific. 

Coloured Bodies. 

For convenience we may study the substances which we 
know as ** coloured bodies,'' under two headings — (a) opaque 
bodies, (/8) transparent bodies. The former owe their colour 
to the phenomenon known as irregular reflection, and to the 
fact that this irregular reflection is usually of a selective 
nature. The ordinary phenomena of reflection which obey 
the two well-known laws — viz., (1) that the reflected ray lies 
in the plane of incidence ; (2) that the angle of incidence 
and the angle of reflection are equal — are known as regular 
reflection. These phenomena do not render objects visible 



10 CHEMISTRY OF PIGMENTS. 

at all, but merely give images of surrounding objects. In- 
deed, the reason that an ordinary mirror surface is visible 
is that a small quantity of diffused or irregularly reflected 
light is emitted. This diffused or irregularly reflected light 
consists of rays reflected in all directions, which do not 
apparently obey the two above-mentioned laws owing to at 
least two reasons : (1) on account of the small irregularities 
of surface, and (2) on account of partial absorption and 
internal reflection ; and to these the visibility of the object is 
due. Now, a body which (irregularly) reflects all the rays 
of the spectrum in the same proportion as they are pres- 
ent in the incident light will appear of the same colour as 
that light. The majority of bodies, however, reflect some 
rays in greater proportion than others, their colour being due 
to the mixture of reflected rays. From these remarks it will 
be seen that the colour of a given body depends on two chief 
circumstances, (a) the inherent selective action which a given 
body has for definite rays, which is constant for a given body ; 
{B) the composition of the light falling on the body. The 
colours we assign to given bodies are always those which 
they possess when the incident light is white. Thus a body 
which absorbs the blue, green and yellow rays of the 
spectrum and reflects the red rays presents the appearance 
we know as red when the incident light is white. But 
when the majority of red bodies are examined in, for 
example, the yellow light of the sodium flame, their colour is 
a dull brown, on acccount of the fact that the amount of red 
rays falling on the body is so small that the reflected light 
contains a correspondingly few red rays, and the observed 
colour is made up of the small number of rays of different 
colours which the body is able to reflect. The usual form, 
from our point of view, of opaque-coloured objects with 
which we have to deal is that of coloured powders. But to 
discuss these it is necessary to understand the cause of colour 



INTRODUCTOBY. 11 

in transparent bodies. A transparent body when examined 
by transmitted light is coloured if it is more transparent to 
some rays than to others, its colour depending entirely on 
the nature of the transmitted rays, or, in other words, is due 
to the absorption of certain rays dependent on the nature of 
the substance itself. Many transparent substances appear of 
different colours when different thicknesses are examined. 
For example, a solution of chromic chloride is green when 
light is allowed to traverse a thin layer of the solution, but 
when the thickness of this layer is increased the colour 
observed is a reddish brown. Such substances are termed 
dichroic. In such a case as this, certain rays are only partly 
absorbed, and the substance must be of a certain thickness 
before the absorption is complete, the colour, of course, being 
due to the residual transmitted rays. When two pieces of 
different coloured glass are examined together by transmitted 
light, the colour observed is not by any means £he mean of 
the two, nor is it the sum of the two colours. As the colour 
is due to the transmitted rays only, it is dependent on those 
rays which both pieces of glass allow to pass. Thus a piece 
of red glass allows light to pass through which consists 
almost entirely of red rays. Green glass, on the other hand, 
allows practically no red rays to pass through. Hence a 
combination of red and green glass will be almost opaque to 
the observer. Again, light transmitted through blue and 
yellow glasses will in general be green — not because blue and 
yellow mixed form green, as is popularly said ; but because 
most yellows and blues when spectroscopically analysed are 
found to contain a large amount of green rays, and it is the 
green rays which both these colours transmit to the almost 
entire exclusion of the other rays. Very few transparent 
bodies are perfectly opaque to any rays. These are usually 
transparent to a very high degree for that one set of rays 
which dominates the observed colour, and allow other rays 



12 CHEMISTBT OF PIGMENTS. 

to pass in small amount. These other rays, of course, 
modify the colour according to their nature and quantity. 
We may now return to the subject of coloured powders, 
which, of course, form the vast majority of pigments in 
everyday use. In a coloured powder every small particle 
must be regarded as a small transparent body capable of 
rendering light coloured by selective absorption in the sense 
we have just detailed. It is quite true that powdered pig- 
ments when taken in bulk are very opaque indeed, but nearly 
every substance when examined in extremely thin layers is 
found to be fairly transparent, and upon this transparency 
their colour effects depend. When white light falls on such 
a powder a small portion of it is reflected from the outside 
surface of the particles ; the remainder penetrates the 
particles and undergoes reflection at some of their surfaces 
of separation. The small portion which is reflected from the 
immediate outer surface is white, as no absorption has 
occurred, but that which is reflected after absorption is that 
which determines the colour ; and since given substances 
possess definite selective ability, the reflected rays are fixed 
for a given substance in a given physical condition. It now 
becomes easy to understand the reason of the alteration in 
the colour of mixed powders. A mixture of green and blue 
powders does not appear green because green is the colour 
situated between the blue and yellow in the spectrum, but 
because the blue pigment absorbs the red, orange and yellow 
rays and the yellow absorbs the violet and blue. Hence the 
only colour which is reflected by both of them is the green, 
which reaches the eye as such' Many common phenomena 
of the painter's art are easily explained in the light of the 
above statements. For example, we all know that a coarsely 
ground powder is more deeply coloured than the same 
powder very finely ground. The quantity of light returned 
at each successive reflection depends on the number of 



^ 
^ 



INTRODUCTOBY. 13 

reflections. If the particles are large the lighir has to pene- 
trate so much the deeper in order to undergo a given number 
of reflections, and more light will therefore be absorbed, and 
the resulting colour will appear deeper. The finer the 
particles the more white light is there reflected at the surface 
before any penetration occurs. A very good example of this 
is the white froth of a deeply coloured liquid. Again, the 
reflection at the surfaces of particles is much weakened by 
interposing between them a fluid whose refractive index is 
nearer to that of the particles themselves than that of air is. 
Pigments are thus rendered darker by wetting them with 
water, and still more so by using the highly refracting oils. 
Much less white light is reflected, and the colour appears far 
darker. This explains the characteristic differences between 
crayon drawings, water colours, and oil paintings {vide infra). 
We have said that the light reflected from the extreme 
outside surfaces of particles is white, but there are certain 
exceptions to this rule, and some bodies appear to reflect 
certain rays by selection in preference to others. Such 
bodies are said to possess surface colours. Many of the ani- 
line dyes are of this nature, and appear of different colours 
when examined by transmitted and by reflected light. The 
colour when seen by reflected light is determined (1) by the 
normal irregular reflection, (2) by the abnormal reflection of 
the selected rays which have been entirely refused admission 
into the particles. The colour examined by transmitted light 
is determined (1) by the absence of the abnormally reflected 
selected rays mentioned above, (2) by the rays which are 
absorbed in the body of the particles. A very well marked 
example of this is the aniline colour, fuchsine. This appears 
of a metallic green colour by reflected and of a rose red 
colour by transmitted light. Incidentally we may mention, 
as illustrating the dependence of colour phenomena on 
external circumstances, that the solution is peacock blue 



14 CHEMISTRY OF PIGMENTS. 

when examined through a polarising prism, but the explana- 
tion of this is outside the scope of the present work. 

The proper study of colour effects and mixtures is de- 
pendent on a knowledge of the exact selective power of 
various substances. This property is only to be exactly 
understood by the examination of the absorption spectra of the 
bodies in question. When a pure solar spectrum is examined, 
it is seen to be crossed by a number of dark lines, usually 
known, as mentioned above, as Frauenhofer's lines. Each 
wave produces its own image of the slit of the spectroscope 
in its proper position, according to its refrangibility, and in 
a spectrum of an ordinary incandescent body, which is not 
traversed by any dark lines, the wave lengths differ in so 
gradual a manner that the various images are extremely 
close together and the spectrum appears contintums. We 
must not assume, however, that light rays of every possible 
refrangibility are present because a spectrum is continuous. 
It is more correct to say that all wave lengths are present, 
within the limits of the resolving power of the best 
instruments we possess; and were it possible to construct 
spectroscopes of infinitely greater resolving power than the 
best we now possess many continuous spectra might become 
discontinuous. The black lines observed in the solar spectrum 
indicate the absence of the rays of refrangibilities corre- 
sponding to the positions of those lines. To be correct, we 
should not say that these rays are completely absent, but 
they are so nearly so that they appear black by contrast with 
the other brilliant illumination. These dark lines are found 
to be in the exact positions of the brilliant bands emitted 
by certain definite incandescent vapours. For example, the 
well marked D line of the solar spectrum (or, more correctly, 
D lines, as powerful spectroscopes will effect this resolution) 
is identical in position with the brilliant yellow sodium line 
seen when sodium vapour is incandescent. The explanation 



INTBODUCTORY. 15 

of these dark lines is that the inner mass of the sun emits 
the hght which gives a continuous spectrum. This, however, 
has to pass through certain cooler vapours on the outer 
surface, and these absorb each its own special rays almost 
entirely, thus accounting for the absence of these rays in 
the solar spectrum, as we see it. In this manner a very 
large number of elements have been shown to be present 
in the sun's vapour. 

These continuous or discontinuous spectra are produced 
by luminous bodies, but colouring matters are not in them- 
selves luminous, and to produce their absorption spectra we 
must allow light to traverse a glass vessel containing a 
solution of the colouring matter, before reaching the slit 
of the spectroscope. The spectrum now observed will be 
found to be traversed by one or more dark bands of varying 
width, the colour bands observed being constant for definite 
bodies under given conditions. The absorption spectra of 
bodies may be graphically represented either by shading 
the dark bands according to the degree of absorption on a 
continuous spectrum diagram, or, better, by indicating the 
spectrum by a horizontal line (abscissa), and the intensity 
of the absorption at each point by means of vertical dis- 
tances from the abscissa (ordinates). The resulting curve 
at once gives an extremely comprehensive grasp of the 
properties, of the colour. It will now be convenient to give 
an account of the absorption spectra of a number of bodies 
of various colours, starting, say, from the red end of the 
spectrum. 

Azorubine. — This body is one of the coal-tar dyes of the 
diazo series, known chemically as sodium naphthalene sulphonate 
azo-a-naphtol sodium sulphonate. It is a full crimson colour, sup- 
pressing practically all rays except the extreme red (Fig. 3, 1). 
Scarlet B belongs to the same group of compounds, and 
is sodium xyl&ne-azo-^-naphtol sulphonate. It is a fine scarlet 




16 CHEMISTBT OF PIGMENTS. 

colour, and its absorption spectrum shows that it allows prac- 
tically nothing but the red and a portion of the yellow-orange 
rays to pass (Fig. 3, 2). 

Alizarin, — This body is the essential colour-bearer of the 
well-known madder plant, but is now practically entirely 
produced synthetically from anthracene, one of the hydro- 
carbons present in coal tar. It is a dioxyanthraqmnone. This 
fine red colour gives absorption spectra, which do not mate- 
rially differ if the solvents are neutral, but which are by 
no means identical when acids or alkalies are added. Several 
of these are given here, from which it will be seen that all rays 
as far as the D line are fairly freely transmitted in all cases 
(Fig. 3, 3). 

Eosin. — Typically pure eosin of commerce, which is usually 
sold as Eosin J, is the hydrated potassium salt of tetrabromo- 
fluorescein, of the formula CgoHeBr^OgKg + GHgO. Mixtures 
of this body with the analogous dibromo-compounds are sold 
as Eosin 5 G, and have a more orange shade, and various 
closely related compounds of lighter or darker shades are 
common articles of commerce. The appended spectrum is 
that of the typical compound in (a) concentrated, (^8) dilute 
alcoholic solutions (Fig. 3, 4). 

Tartrazine, — This well-known colour is the sodium salt 
of disulphO'diphenylizine-diooDytartaric acid. It is an orange 
yellow powder which produces a fine yellow colour with a 
reddish tint. Picric Acid, or trinitrophenol, is a typical 
colour yielding a much yellower spectrum than tartrazine. 
The two are here illustrated (Fig. 3, 5). 

Acid Green is the typical name of a number of coal-tar 
greens, which are sulphonic acids of the various aldehyde 
greens. Of these the ordinary Helvetia green is one of the 
most common. The spectrum given shows that the whole 
of the red and yellow and much of the violet is totally ex- 
tinguished, with the result that a brilliant green (with blue 
in it) results (Fig. 3, 6). 



INTRODUCTORY. 



17 



Indigo. — The spectrum yielded by indigo extract varies 
to a small exteht according to the exact method of prepara- 
tion of the extract. But these variations are only slight, and 
the chief feature of a typical extract, which is shown below, 
is the almost complete extinction of the red-yellow rays and 
the extreme violet (Fig. 3, 7). 

Methyl Violet. — The last spectrum we shall here consider 
is that of methyl violet, one of the coal-tar violets, whose 
chemical relationships are expressed by the name pentamethyl 
pararosaniline hydrochloride. The total extinction of nearly 
the whole of the red, all the yellow and all the green rays i& 
the characteristic of this spectrum (Fig. 3, 8). 

A BC D E F G H 









I 




1 






1 


^ 


• 
























2 
















^^ 




•^ 


c::^-^3I 




3 


___— - — 


4 






Y 


B ^ — 1 

r/ 


^ 


^ 










B O 


^= 






5 














■N 


OB 


^ 




6 






* 






^ 


L- 


-^ 


V 




r 




7 


r- 


8 






/ 


"'V^ 


* 







Fig. 3. 

3. a Alcoholic solution. 

)3 Alcoholic ammoniacal solution. 

y Aqueous ammoniacal solution. 
5. a Tartrazine. 

)3 Picric acid. 



2 



CHAPTEK II. 

THE APPLICATION OF PIGMENTS. 

In deciding the relative suitability of pigments for any parti- 
cular case two sets of circumstances must be taken into 
consideration : on the one hand, the purpose for which 
the pigment or pigments may be required, whether purely 
artistic, decorative or protective, and the conditions under 
which this purpose must be fulfilled ; and, on the other, 
the nature of the pigments and of the media and methods of 
application at the worker's disposal. These circumstances 
having such an important bearing on the chemistry of pig- 
ments, we have thought it advisable to consider them before 
proceeding to the systematic description of the pigments 
themselves. 

I.— USES OF PIGMENTS. 

(A) Purely Artistic Uses. 

These include all those various methods of depicting 
objects and events in colours which have been recognised 
as most suitable when accuracy of representation, whether 
imitative or suggestive, has been the principal object sought 
to be attained. It is obvious that this is the highest use to 
which colours can be put, and in many respects the most 
exacting in its requirements, the more general of which, as 
applying equally to all branches of pictorial art, we will now 
consider. 



THE APPLICATION OF PIGMENTS. 19 

Whatever surface may be adopted for the reception of 
the picture, and in whatever manner it may be decided to 
apply and fix the colours on that surface, it is evident, in the 
first place, that the relations of surface and colour must be 
such that the masses of colour applied may be distributed 
in any form that is necessary for depictive purposes, and, 
whether the work is in natural colours or monochrome, shall 
be capable of all gradations of shade or intensity, from the 
full density of the colour to the merest suggestion of the 
same. 

In order that this quality of ** workability *' may be 
possessed in the highest degree, it is necessary that the 
pigment be in a very fine state of division, and uniformly 
diffused throughout the medium by means of which it is 
applied, and that some means of dilution can be adopted, 
either by the addition of a white pigment in the case of 
''body colour," or by increasing the proportion of medium 
or the application of the colour in very thin layers in those 
cases in which the colour is used as a " stain" or '* glaze ". 
This fine state of division is obtained by various processes of 
crushing, grinding, occasionally by roasting and washing or 
levigation. The latter method is particularly valuable, as 
particles which could not be separated by the finest sieve 
can be suspended in water and the finer matter, after the 
coarser particles have settled to the bottom of the vessel, 
run off with the water and allowed to slowly deposit, the 
coarse particles being again ground. All these processes of 
preparation of powders are described in various technical 
w^orks, and need not be considered at length. It is not 
now the general custom for artists to prepare their own 
colours, though before the rise of a special industry this 
vsras necessarily the case. In this respect, at any rate, 
modern artists are more fortunate than their predecessors, 
as doubtless specialised machinery is more effective than 



20 CHEMISTRY OF PIGMENTS. 

the more primitive appliances of earlier ages, and time is 
not wasted in purely mechanical operations. It is possible, 
however, that in some other respects the wholesale prepara- 
tion of artists' colours is not an unmixed boon. The question 
of media or colour vehicles will be discussed in another part 
of this chapter ; for the present it is sufficient to predicate 
of the medium that it shall have no immediate appreciable 
effect on the appearance of the colour, and in most cases 
that after the colour is effectually fixed on the receptive 
surface its tint shall remain unaltered, or that in special 
cases the effect shall be certain and easily estimable. 

Granted the possession of the quality of workability, it 
is necessary that the colours at the artist's disposal be 
iris-hued, capable either separately or judiciously mixed of 
imitating the colour or the colour effect of any object which 
the eye has seen or can conceive. Unless this is so artistic 
effort must be confined to monochrome (which, though giving 
considerable scope for a master of form and light and shade, 
has, it must be confessed, much the same effect on the eye 
as a Gregorian chant in music, or a very severe adherence 
to a very obvious metre in poetry, has on the ear), or to a 
very crude colour scheme which is less pleasant and certainly 
less artistic than monochrome. In this respect, so far as 
the representation of objective effects are concerned, our 
known pigments leave very little to be desired, as an examin- 
ation of the works of the great pre- and post-EaphaeUtes 
(and Eaphael himself) of the Italian schools, of the Dutch 
school, especially some of the still-life examples, and, though 
last, not, in mstny respects, least, of our great English land- 
scape painters, and of those two masters of atmospheric 
effect, Claude and Turner, will convince one. The suggestion 
of the subjective phenomena of interference and diffraction 
colours has indeed not presented insuperable difficulties to 
some of our colourists. It is not, however, sufficient for the 



THE APPLICATION OF PIGMENTS. 21 

highest kind of artistic work that colours should be capable 
of easy application to the prepared surface and be sufl&ciently 
diverse and brilliant for purposes of imitation, but, in justice 
to the labours of the artist, they must, under reasonable 
conditions, be permanent. In this respect the artist is, rela- 
tively to the poet or musician, very unfortunately placed in 
regard to posterity ; the effect sought to be produced by either 
of the latter is entirely independent of the manner of repro- 
duction. The writings of Homer, Shakespeare or Milton, 
the musical compositions of Palestrina, Purcell, Ahn or 
Mozart, and those fragments of ancient music we possess 
are not only (except for corruption of text or score) in the 
same verbal form as the original copy issued from the 
author's hand, but, thanks to writing, musical notation 
and printing, capable of indefinite reproduction. By reason 
of this fact there seems no reasonable possibility of such 
works being either lost or, saving for alterations of taste and 
habits, failing to produce the same emotions and sensations 
as they have always been capable of doing. With the artist 
things are entirely different, he appeals to the feelings, not 
through the ear, nor through the eye as a mere signalling 
instrument, but through the eye in all its powers of convey- 
ing sensations of form, colour, light and shade ; his work, as 
laborious, as poetical as that of the writer or composer, can- 
not be reproduced in such a way as to convey its full effect, 
and consequently he can only appeal to a limited number 
of people (and only in one place). Not only is this the 
case, but he is working with materials the entire suitability 
of which can never be satisfactorily determined, for whereas 
we can decide that such a work is fading, or the surface 
cracking, or the high lights going, and so being lost to 
posterity, we can never be sure that another work now in 
good preservation may not in the future show signs of such 
decay. The materials used by artists are also only perman- 



22 CHEMISTRY OF PIGMENTS. 

ent when properly kept, so the safe custody of the one only 
example of each work of the artist becomes a matter of the 
highest moment. 

The ideal of permanence required of artists' colours is very 
comprehensive. The surface must not only remain intact in 
spite of the action of air, moisture, light and some variations 
of temperature (not usually great), but all the colours must 
retain to a very great degree, if possible to the end of time, 
their original tint, however delicate. The bright colours and 
the high lights must retain their brilliance, and the darker 
colours and shadows their obscurity, or the contrast of light 
and shade, the chiar*oscuro as it is called, will be destroyed, 
and the objects which, when the picture left the painter's 
hands stood out, as it were, from the picture, and those which 
were in the distance, appear to be but little separated, and 
the whole seems flat and lacking in atmospheric effect. 

That this permanence of colour and shade has been very 
closely approximated to by many old masters is shown on an 
examination of their works. The earliest examples in the 
National Gallery are a series of portraits, either Greek or 
GraBco-Eoman, taken by Mr. Flinders Petrie in 1888 from 
mummy cases discovered in an ancient cemetery at Hawara 
in the Faj^tim, Egypt. Ten of these are painted on wood 
panels in the encaustic method, the remaining one being 
apparently in tempera on canvas ; this specimen is not in 
very good preservation, rather the result of rough usage than 
natural deterioration. The others are still pleasing looking, 
the flesh colours being fairly good, and the white used for 
some of the draperies and high lights, two shades of 
(Tyrian?) purple, blue and crimson drapery, blue, red and 
green stones, set in gold, and other gold ornaments retaining 
sufficient of their original brilliancy to be convincing. Alto- 
gether, these ten pictures well illustrate the permanence of 
colours in so inert a medium as wax, though it must be 



THE APPLICATION OF PIGMENTS. 23 

borne in mind that from the nature of the case the portraits, 
being preserved in the dark and in the dry atmosphere of 
Egypt, had everything in their favour. It remains to be 
seen what effect the light of a gallery and our moister climate 
will have on them. A painting by Margaritone (died 3293), 
in the conventional Byzantine style, of " The Virgin and 
Child,' with Scenes from the Lives of the Saints '* (No. 564) 
is not at all satisfactory. The colours are very dingy, and in 
some cases absolutely changed beyond recognition. The 
picture is in tempera on linen fastened to wood, and it is 
probable that part of the dark appearance is due to the 
unsatisfactory medium used. A painting — school of Giotto 
{circa 1330), who introduced white of egg as a medium — of 
*' The Coronation of the Virgin '' (No. 568) is still in very 
good preservation. The iris-hued wings of attendant angels, 
a green and a scarlet, still look fairly bright. Another 
painting of the same subject by Orcagna (died 1368), in 
which a great many figures are represented, shows such 
varied colours as crimson, scarlet, green and blue in very 
good preservation, and some very varied and pleasing flesh 
tints, from the delicate pink of the principal figures to quite a 
swarthy sunburnt hue. The swords in the hands of some of 
the saints, however, look very black, probably owing to 
serious changes in the pigment used. '*A Baptism** by 
Taddeo Gaddi (died 1366) shows the following colours : two 
purples, crimson, a bright red, a colour like raw sienna, a 
sage green, blue, and two flesh colours, coarse and delicate, 
and the steel of a sword, all but the latter satisfactory. A 
''Virgin and Child" (No. 283) by Gozzoli (died 1498) shows 
good flesh tints, and two goldfinches still looking well 
coloured. His ** Eape of Helen " (No. 591) shows good flesh 
colours, scarlet and blue; the landscape, with sea forming 
the background of this, is fairly good, but the green (probably 
vegetable) of the trees is very dull. Sandro Botticelli (died 



24 CHEMISTEY OF PIGMENTS. 

1510) is represented by six pictures, all in tempera : No. 275, 
** The Virgin and Child, St. John Baptist and an Angel,'' is 
perfect in colour, the principal colours being delicate and 
swarthy flesh tints, and gold (brocade). No. 626, ** Portrait 
of a Young Man in Brown Dress and Light Bed Cap," 
is characterised by a rather tallowy (perhaps accurate !) 
flesh colour and a fine red. No. 915, **Mars and Venus 
and Four Young Satyrs," shows a very wide range of 
colours ; very varied flesh tints, delicate for Venus, sv/arthy 
for the satyrs, white, gold, crimson, steel (armour), a reddish- 
brown conch shell and the dark rich green of the myrtle, a 
very fine picture. By the side of this is a picture (No. 651), 
''Venus, Cupid, Folly and Time," by Bronzino (died 1572) 
in which varied flesh tints, blue draper}^ a russet apple (of 
Discord), red roses, a crimson cushion and the white doves 
of the Paphian goddess appear with a remarkable freshness. 
*'A Virgin and Child" and a ''Virgin Adoring the Infant 
Christ," by Lorenzo di Credi (died 1537), show a brilliance of 
colouring both of the figures and drapery and of the landscapes 
in the distance which time would have done well to soften, 
though in their way they are perfect. The " Portrait of Julius 
IL" (No. 27), "St. Catherine of Alexandria" (No. 168), the 
Garvagh and Ansidei Madonnas and the ancient copy of the 
Bridge water Madonna of Eaphael (died 1520), " The Holy 
Family" (No. 4), " Venus and Adonis" (No. 34) and " Bacchus 
and Ariadne" (No. 35) of Titian (died 1576), "The Portraits 
of Jean Aniolfini and His Wife," by Jan Van Eyck (one of 
the earliest oil painters), painted in 1434, and many other 
works of masters of the early Italian and Flemish schools 
might be quoted as examples of beautiful fresh colouring, 
retaining, so far as may be judged, correct relationship of tone ; 
but as this is a w^ork rather on the materials used by artists 
than on their works, the mention of a few works by masters 
of light and shade and atmospheric effects, which would be 



THE APPLICATION OF PIGMENTS. 25 

entirely marred by the fading of dark masses or the deteriora- 
tion of high lights, must conclude this examination of pictures 
which have stood the test of time. The portrait by (and 
of ?) Andrea del Sarto, Andrea senza errori (Andrea without 
faults) as he is called, would, if the beautiful soft light on the 
cheek or the white of the shirt were to darken, or the shade 
over the rest of the face and the darker background fade, be 
a dull, flat picture, though still beautiful, instead of being, as 
it is, perfect. The ** Agony, after Correggio," with its peculiar 
illumination of the two figures in the darkness, requires abso- 
lute permanency in the high Hghts. The '' Walk to Emmaus," 
by Lelio Orsi (died 1586), is another early work in which the 
whole effect is due to the chiar'oscuro : a burst of light through 
a dark sky lights the figures, throwing the folds of their gar- 
ments and their faces into violent relief and reflecting gleams 
from a dagger hilt and the top of a walking stick. The later 
examples of Eembrandt, especially the marvellous '* Adora- 
tion,'' with its natural and supernatural illumination, the 
heavenly light from the Child and the dull glimmer of the 
shepherds' lantern ; of the Dutch landscape painters (especi- 
ally Hobbema); of the French landscapists, Claude Lorraine 
("Gel6e") and Gaspard Dughet C'G. Poussin "), nearly all 
works depending for their highest beauty on very subtle 
schemes of light and shade and atmospheric effect, most of 
them over two centuries old, tend to show that it is possible 
to produce works of a very high degree of permanence both 
of colour and of tone. At the same time it must be admitted 
that some of the colours used by the earlier masters, as, for 
example, bitumen, were highly unsatisfactory both as per- 
manent colours and on account of their injurious effect on 
the surface ; and again, possibly, a process of natural selection 
has weeded out many once beautiful works from the front 
rank and turned them into the ''speculative pictures" and 
"doubtful old masters " of the auction room and the would- 



26 CHEMISTRY OF PIGMENTS. 

be art patron. It is, notwithstanding, a matter of great regret 
that we do not know more of the methods both of preparation 
and working of the old masters. That we know so little is 
not a matter for surprise ; the secret process is not yet dead 
in chemical works (though it is usually a secret shared un- 
consciously with most other similar works) and the whole 
tendency of the middle ages, a tendency not seriously modi- 
fied by the Eenaissance, was for members of a guild or 
confraternity (of craftsmen) to keep their methods very 
secret, the master not always fully initiating his pupils, far 
less trusting his methods to paper or to his fellow, and rival, 
artists. Though in many ways to be regretted this is very 
natural on the part of those who had probably with great 
labour prepared their colours and discovered secrets they 
did not reveal. The fact, however, remains that of the 
methods of the ancients very little is known ; to attempt a 
chemical examination of the works of acknowledged masters, 
involving as it would their destruction or serious mutilation, 
would be, apart from pecuniary considerations, an act of 
most atrocious Vandalism and would probably be entirely 
unsuccessful, both on account of the small amount of colour 
actually applied to the surface and of the difficulty of such 
examinations, particularly when it is desired to examine the 
nature of the medium employed. It is, to an extent, possible 
to form some idea as to the colours used on a certain picture, 
but this does not always, even if the conjecture be correct, 
convey much information, as permanence may be affected by 
the presence or absence of accidental impurities and depends 
on the pigment, the medium and the surface, even supposing 
conditions of preservation to be the same. The study of 
ancient pictures principally serves to remind us that it is 
possible to obtain and to apply colours that will last for 
centuries and still present to the eye such well-known hues 
as those of human flesh, of sea and sky, and of those animate 



THE APPLICATION OF PIGMENTS. 27 

and inanimate living things which we know have not altered, 
and this not merely in a conventional manner (as the picture 
writing of certain ancient nations), but with that force of 
imitation or suggestion which almost convinces the eye of 
their reality. This test of the fidelity of colour of natural 
objects (making due allowance for the bluish flesh of one 
period, the brown tree of another, and other obvious manner- 
isms) seems, where applicable, the fairest to apply in judging 
of the permanence of colours as colours ; the test of the 
conviction produced by arrangements of light and shade the 
best for that kind of permanence which is the result of fixity 
of intensity or that quality which alone would appeal to the 
colour-blind. 

In the absence of this information concerning the per- 
manent pigments of the earlier painters, and in face of the 
lamentable condition of many modern pictures (particularly 
those of Stothard, and, it is to be feared, some of Turner's 
and Landseer's), the desirability of an extended series of ex- 
periments on the action of light, air, moisture, heat and 
products of combustion is evidently great. Such experiments 
should include an examination of many (analysed) specimens 
of each pigment with a view to determining the influence of 
impurity and of variation of composition, and of the speci- 
mens used in different media on such surfaces as are generally 
considered suitable for the several media. So far as the 
modern and beautiful method known as " water colour," in 
which our countrymen have always excelled, is concerned, 
some most highly interesting experiments have been carried 
out in a manner remarkably free from empiricism by Dr. 
W. J. Eussell and Captain (now Sir) W. de W. Abney, who 
in 1888 presented a report to the Science and Art Depart- 
ment " On the Action of Light on Water Colours ". The 
interest of the report is enhanced by the circumstance that 
these gentlemen were advised and supplied with colours by a 




28 



CHEMISTRY OF PIGMENTS. 



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30 CHEMISTBY OF PIGMENTS. 

committee of water-colour artists, including the late Sir F. 
(Lord) Leighton, Sir E. J. Poynter (now P.E.A.), Sir Alma 
Tadema, Mr. Sidney Colvin and others, and that forty- 
six distinguished artists who used water colours furnished 
the authors with lists of the colours they were in the habit of 
using in their work. 

The authors made a series of experiments with thirty- 
nine colours, in the first place, exposed to the full action of 
air and daylight. " The colours to be tested were applied by 
a practised hand to the paper in a series of washes. ... In 
most cases as many as eight washes were applied, giving thus 
a complete series of eight tints.** These strips were divided 
so as to give two equal strips each with the eight tints ; 
these two strips were both placed in a glass tube open at 
each end and bent at the top, so that, while the complete 
action of air was ensured, the tubes, which were placed 
against a wall facing nearly south, were protected from the 
entrance of wet and dirt. One half of the tube was bound 
round with American cloth in order to protect one strip from 
the action of light. ** The two pieces of identically tinted- 
coloured paper were therefore under exactly the same con- 
ditions in all respects, except that one was exposed to light 
and the other was in the dark.** The papers were exposed 
from May, 1886, to March, 1888, and were observed on 14th 
August, 1886, in December, 1886, and in July and in No- 
vember, 1887, and finally in March, 1888. It should be stated 
that a very careful approximation of the relative illuminat- 
ing powers of bright sunlight, the light from the sky, and 
of diffused light from clouds was made, so that the authors 
were able, knowing the hours of sunshine at Kew and Green- 
wich Observatories during the period of their experiments, 
and taking the mean of these as representing the sunlight at 
Kensington, to state that between May and August, 1886, 
they considered that the pigments received a total illumination 



THE APPLICATION OF PIGMENTS. 



31 



equal to 2,225 hours of average blue sky. " This, of course, is 
only an approximate estimate." They also consider this to 
be equivalent to 100 years in a gallery illuminated similarly 
to those at Kensington. The results of the first and last 
examination of the tints are given in the preceding table 
(Table I. of the Eeport). 

A second series of experiments was made in hermetically 
sealed tubes, with dried tinted paper and dry air. The 
results obtained are epitomised in the following table (Table 
III. of the Eeport) : — 



Name of Colour. 


Dry Air. 


Carinine 

Crimson Lake 

Scarlet Lake 

Vermilion 

Rose Madder 

Madder Lake 

Indian Red 

Venetian Red 

Brown Madder . . . . 

Burnt Sienna 

Gamboge . 

Aureolin 

Chrome Yellow 

Cadmium Yellow 

Yellow Ochre . . • 

Naples Yellow 

Indian Yellow 

Raw Sienna 

Emerald Green 

Terra Verte 

Chrom. Oxide 

Olive Green 

Antwerp Blue 

Prussian Blue 

Indigo Blue 

Cobalt Blue 

French Blue 

Ultramarine Ash 

Leitche's Blue . , 

Permanent Blue 

Payne's Grey 

Violet Carmine 

Purple Carmine 

Purple Ma4der 

Sepia 

Vandyke Brown 

Burnt Umber 


Faded to 7 

Gone to 5 

Faded and darkened 

Gone black 

No change 

No change 

No change 

No change 

Faded to 4 

No change 

Faded to 3 

No change 

No change 

No change 

No change 

No change 

Faded to 4 

No change 

No change 

No change 

No change 

No change 

Faded to 3 

Faded to 5 

Faded to 7 

No change 

No change 

No change 

Faded to 5 

No change 

No change 

Faded and brown 

Faded 

Faded to 4 

No change 

V. si. faded 

No change 

Faded to 4 



s 



32 CHEMISTEY OF PIGMENTS. 

Of thirty-seven, colours exposed to the action of moist air, 
only the following ten withstood the action of light under 
this condition : Indian red, Venetian red, burnt sienna, yellow 
ochre, raw sienna, emerald green, terra verte, chromium oxide, 
cobalt, and ultramarine ash ; both Prussian blue and Antwerp 
blue were entirely destroyed. Of twenty-nine mixtures only 
two were unchanged — ^raw sienna and Venetian red, and 
cobalt and Indian red. 

A further series was made in which the colour was ex- 
posed to the action of moist hydrogen, so as to obviate the 
action of oxygen. Of thirty-six colours '' no less than twenty- 
two remained unchanged; even carmine and crimson lake 
did not alter, neither did madder lake, Indian red, Venetian 
red, brown madder, burnt sienna, chrome yellow, yellow 
ochre, raw sienna, terra verte, chromium oxide, olive green, 
indigo, cobalt, French blue, ultramarine ash, permanent blue, 
Payne's grey, sepia, Vandyke brown, and burnt umber *\ 

Thirty-nine experiments were made with single colours 
exposed in a (Sprengel) vacuum. ** Violet carmine and 
purple carmine slightly darkened ; Prussian blue and purple 
madder and sepia slightly bleached ; but in all cases the 
action was very feeble. Twenty-four experiments were made 
with mixed colours, and the results are of much interest 
and importance. The mixtures containing Prussian blue 
changed, the other colours becoming dominant. Vermilion 
also blackened. With other mixtures hardly any change 
occurred." 

The actions of the electric arc light, of heat without Ught, 
and of the light and products of combustion of coal gas were 
examined, and experiments were also made with body colours 
and with coloured light transmitted through red, green and 
blue glasses ; in this latter series colours exposed under blue 
glass were acted on to almost as great an extent as those 
under white glass, the difference being due to the opacity 



THE APPLICATION OF PIGMENTS. 33 

of the blue glass. This fully confirms expectations based 
on theoretical considerations that the blue rays, from their 
greater oscillation frequencies approximating to those of the 
constituent atoms of substances, cause more decomposition 
than rays nearer the red end of the spectrum. 

The conclusions arrived at by Dr. Eussell and Captain 
Abney from these experiments are that-^ 

** Mineral colours are far more stable than vegetable 
colours, and amongst those colours which have remained 
unaltered, or have only very shghtly changed after an ex- 
posure to light of extreme severity, a good gamut is available 
to the water-colour artist. . . . 

** The presence of moisture and oxygen is in most cases 
essential for a change to be effected even in the vegetable 
colours. ... It may be said that every pigment is per- 
manent when exposed to light in vacuo. . . . 

*' The effect of light on a mixture of colours which have 
no direct chemical action on one another is that the unstable 
colour disappears and leaves the stable colour unaltered 
appreciably. 

" Our experiments also show that the rays which produce 
by far the greatest change in a pigment are the blue and 
violet components of white light, and that these, for equal 
illumination, predominate in light from the sky, whilst they 
are less in sunlight and in diffused cloud light, and are 
present in comparatively small proportion in the artificial 
Ughts usually employed in lighting a room or gallery. The 
experiments have also shown that about a century of ex- 
posure would have to be given to water-colour drawings in 
galleries lighted as are those at South Kensington before 
any marked deterioration would be visible in them, if painted 
with any but the more fugitive colours ; and that when the 
illumination is of the same quality as that of gaslight, or of 
the electric glow light rendered normally incandescent, and 



w 



34 CHEMISTRY OF PIGMENTS. 

of the same intensity as that employed in those galleries, an 
exposure to be reckoned by thousands of years would have to 
be given to produce the same results. We have not taken 
into account the action, if any, which might arise from the 
products of combustion where gaslight is the illuminant, and 
which our experiments so far have shown to have but 
a trifling effect, nor of any modification of hue which might 
be due to change in the whiteness of the paper on which the 
paintings were made, but simply to the change in the colours 
themselves." 

A suggestion as to the use of yellowish glass in galleries 
is also made in this report. 

(b) Decorative Uses. 

Under this heading we must include all those applications 
of pigments in which the suitable adornment of useful or 
quasi-useful objects is the principal purpose to be served, 
considerations of pictorial accuracy or effect or of protection 
of surface being subordinated to this in a greater or less 
degree, according to the peculiar circumstances of the case. 
These applications would comprise all kinds of mural decora- 
tion, including coloured-glass windows, the adornment of 
keramic ware of all kinds, of glass and of indoor (to a certain 
extent of outdoor) woodwork, and in some cases of metal 
work ; the media employed in these cases are, of course, most 
varied in their nature. 

The requirements of pigments to be used for decorative pur- 
poses are, naturally, somewhat allied to those of the artist on 
the one hand, and to those of the strict utilitarian on the other. 
A choice — not so great as the artist demands, for the decora- 
tor's depictive efforts are more conventional than imitative — 
of colours is obviously needful, as is also permanence of rather 
a different kind to that to which the artist endeavours to 
attain. The conditions under which decoration is employed 



THE APPLICATION OF PIGMENTS. 35 

are usually more trying, both as regards atmospheric and 
other influences, because decoration is, after all, necessarily 
subordinate to human comfort and convenience. A painted 
ceiling, however lovely, is the top part of a room which 
should serve a useful purpose ; a beautiful vase, however 
useless, is the descendant, though perhaps very remote, of a 
jar used to hold water, corn, or wine, or oil, or some other of 
the possessions of early communities, and still in many ways 
approximates to these more useful members of its family ; a 
stained-glass window should be a means of letting in light 
and keeping out rain and wind from a building ; a painted 
panel of a door or cabinet is primarily part of a structure, and 
though in many cases these things have been used by the 
artist as means by which he can exercise the pictorial art, 
they cannot be considered as the most suitable. The kind of 
permanence, therefore, required is rather of surface than of 
tint. A colour which will adhere well to the material and 
allow of the surface being cleaned, will, if it retain its tint 
fairly well, be preferable to one which, retaining its tint 
better, is more susceptible to atmospheric influences or 
wear. 

It must be borne in mind that, whereas the pictorial artist 
subordinates his surface and methods to his subject, choosing 
the most suitable surface and medium, he who seeks to excel 
in decoration must adapt everything to the surface or thing 
to be decorated ; the colours, the medium, must be such as 
on a certain object will produce the best effect and most en- 
during. The question of cost is also, considering the often 
extensive nature of such work, one which must not be 
neglected ; also a due sense of proportion must be exercised in 
deciding 'to what extent perfection and permanence are likely 
to be required, or elaborate and costly schemes justified. 

As the suitability of pigments for this class of work so 
much depends on the nature of the surface to be decorated 



V 



36 CHEMISTRY OF PIGMENTS. 

and the consequent colour-vehicle to be employed, it will be 
more convenient to consider the matter under the heading of 
methods employed in applying pigments rather than in this 
place; it always being remembered that the perfection to be 
sought in this sort of work is not of that absolute kind which 
is always desirable for serious artistic work, except in the 
very highest kind of decoration, which, in our opinion, is only 
legitimate in those cases where the permanence and proper 
treatment and receptive condition of the building or structure 
to be decorated can be well guaranteed. A painted ceiling, 
which is quite legitimate at Hampton Court or Greenwich, 
where the conditions are favourable, might be prepared and 
executed with much more costly and carefully selected pig- 
ments, media and surface than would be justifiable in a 
private house, which is liable to demolition for local improve- 
ments, or to premature senile decay. (What is true of 
materials is still more true of the worker !) 

(c) Protective Uses. 

From the purely utilitarian point of view these are the most 
important uses to which pigments may be put. The principal 
materials treated with paint for this purpose are wood arid 
iron, and such treatment in each case becomes necessary 
only when exposure to moist or otherwise specially active air, 
or to water, is liable to cause deterioration of the surface with 
its subsequent general decay ; and in the case of wood when 
it afifords an easily cleaned surface. So far as we know, wood 
or iron exposed to perfectly dry air would be unaltered for an 
infinitely long period, but as this cannot be the case with 
articles in common use, or exposed to the weather, or im- 
mersed in water, the use of paint or varnish must be resorted 
to in all work that is intended to be of a permanent character,, 
except, perhaps, in the case of very hard woods, which often 
have very high weathering qualities. 



THE APPLICATION OF PIGMENTS. 37 

The object of painting or varnishing iron- or wood- work 
is, apart from considerations of appearance, to form a surface 
coating, impervious alike to air and water, which will prevent 
iron from rusting and wood from becoming waterlogged, 
swelling, and perhaps, on drying, cracking, and in course 
of time becoming rotten, water and air having no action, 
either direct or indirect, on the surface.^ This coating in 
many cases, as ships' sides and iron- and wood-work and all 
work which must be handled much, must be not only 
impervious but tough, and not easily rubbed off, and in all 
cases must be fairly permanent, so that renewal is not 
frequently necessary ; this is especially the case in large 
engineering work, where the difficulty of getting at the parts 
of a structure is often great. 

Protective applications for such work may be considered 
under the following groups : — 

(1) Asphaltic varnishes. 

(2) Oil varnishes. 

(3) Paints. 

(a) Presumably inert to the medium in which used. 

{b) Active in forming a varnish with the medium. 

(c) Antifouling by reason of their own erosion. 

Concerning the relative value of members of the above 

groups opinions vary greatly, and, unfortunately, in this, as- 

in many other cases, opinion has been allowed to take the 

place of definitely ascertained facts : a certain coating has 



^ It seems probable that many substances are less protective than might, 
at first, be expected when applied to metal-work, owing to one or both of the 
following reasons : (a) small quantities of soluble salts are through faulty 
preparation contained in the pigment which may either act directly on the 
surface in the presence of moisture, or which may absorb water and, producing 
minute crystals of different volume and form from the original salt, tend to 
weaken the coating by mechanical action ; (b) the pigment may contain 
constituents which are decidedly electro-negative to the metal coated, and so 
set up electro-chemical action with erosion of that metal. 



38 CHEMISTBY OF PIGMENTS. 

done well under one set of conditions, and is therefore con- 
sidered by its user as the protective coating par excellence, 
while another coating, under totally different conditions, is 
found by another individual to be satisfactory, and he is of 
opinion that this is the material to be used in all cases. Some 
attempts have, however, been made from time to time by 
chemists and engineers to attack the problem of protection of 
iron-work from some other standpoint than the mere weather- 
ing of some isolated iron structure, possibly under abnormal 
conditions. A paper, in which most of the work done in this 
direction is examined and discussed, and a new series of 
valuable experiments described, was read by Mr. Harry 
Smith, F.I.C., before the Newcastle Section of the Society 
of Chemical Industry in December, 1899. 

It would appear from this paper that most writers on the 
subject agree (1) that the work to be treated should be as 
clean and free from scale as possible ; this to begin with 
ensures the absence of any particles much more electro-nega- 
tive than iron ; (2) that a treatment with hot (or cold) linseed 
or boiled linseed oil is desirable both as a protective coating 
and for the paint to adhere to more firmly than it will to the 
untreated iron (Mr. Smith's and some other experiments do 
not show this). Beyond these two points there is very little 
agreement on the part of the various experimenters, as the 
following quotations will show : — 

Iron oxide paints adhere better to Iron oxide paints should not be 

ironwork than lead paints. Asphal- used on iron, as the pigments them- 

tum paints are not satisfactory. selves act as carriers of iron and 

E. Gesleb. produce rusting. 

A. H. Sabin. 

The red paint known as oxide of ^oltze obtained the best results 

iron, and which was claimed to be ^jt^ genuine asphalte varnishes, 
a rust preventative, possesses no in- 
herent quality of that kind. 

Engineer, 

The method of experimenting adopted by Max Toltze, and 



THE APPLICATION OF PIGMENTS. 39 

later by Mr. Smith himself in his second series of experiments, 
was as follows (Toltze's description) : — 

** The iron dishes were about twelve inches in diameter 
and about half an inch deep, having a capacity of about half 
a pint. The scale or skin was carefully removed before 
painting, so as to have a clean surface of iron exposed to 
the paint. Two dishes were painted with each kind of paint, 
one of them receiving one coat, the other two coats, the first 
coat having dried thoroughly (for at least a week) before the 
second coat was applied. After the second coat had com- 
pletely dried and hardened these dishes were exposed to the 
so-called water-and-moisture test, in which a given amount 
of water is placed in the dishes and allowed to evaporate to 
dryness at the ordinary temperature of the room. This is 
repeated a number of times until the inside of the dishes 
begins to show more or less rust. All dishes were carefully 
examined before each refilling. After most of the water has 
evaporated there remains at the junction round the edge a 
thin film of water, which, in contact with the carbonic and 
other acids in the air, acts on the paint in such a way that the 
iron under the paint begins to rust. The rust thus formed 
develops more and more after each evaporation, in some cases 
practically covering the whole dish in a short period." 

Mr. Smith carried out experiments with forty-nine dif- 
ferent preparations under the conditions described hereunder 
by himself :: — 

" The tests were carried out in three different ways : — 

" 1. By painting shallow iron dishes and exposing them to 
the action of slowly evaporating water as described in Mr. 
Toltze's experiments quoted above. 

'' 2. By exposing a set of painted iron plates to the con- 
tinuous action of the weather for a period of twelve months ; 
and 

"3. By. exposing painted iron plates to the continuous 



40 CHEMISTRY OF PIGMENTS. 

action of water in a similar manner to the tests made by 
Mr. Thomson and myself in 1894. 

** 1. The paints employed were prepared by grinding the 
pigments with linseed oil on granite rollers to a stiff paste 
in the proportions given below; these were thinned to the 
consistency of ordinary paint with boiled linseed oil of the 
best quality, and capable itself of yielding a dry film on a 
glass plate in about seven hours under ordinary conditions 
of temperature, etc. 

**Each plate or dish was given two coats of paint, the 
second being applied after the first had become thoroughly 
dry ; the tests were commenced when the second coats all 
appeared to be dry and firm. 

''Let us take the dishes first. Each dish was about 
five inches wide by half an inch deep, and was filled with 
ordinary town water ; they were placed side by side upon a 
table, and were not touched during the three months over 
which the trial extended ; but as soon as the water had 
completely evaporated from each dish it was immediately 
refilled with fresh water. During the three months each 
dish dried and was refilled six times. 

**In most cases all traces of paint have disappeared, and 
there is present a thick deposit of rust mixed with the sus- 
pended and soluble impurities present in the evaporated 
water. 

** The dishes painted with the following paints are 
practically unaffected, and have withstood the very severe 
conditions of the trial : — 



Bed lead paint \ 
* A ' Bed lead paint 
*B 

Orange lead 
Vermilionette 
Scarlet red 



>i >» >» 
>» 

11 



y 



Practically unaffected. 



THE APPLICATION OF PIGMENTS. 41 

" The folloYnng are slightly rust-stained, and are placed 
in order of merit. 

Zinc white (oxide) paint 
* A * Zinc white 



Lithopone 
White lead 
*A' 



f) 
ft 
ff »i »» 



^ Slightly rust-stained ; placed in 
order of merit. 



If ff ff 



/ 



"As to the thirty-six other paints tried in this way, all 
appear to have suffered equally ; but it was noticed that 
the dish painted with boiled Unseed oil simply was the 
first to show deterioration, and has apparently produced 
"the greatest amount of rust. 

'' 2. The forty-nine iron plates, which were painted and 
•exposed to weather for twelve months, all stood this test 
remarkably well, showing that all the paints were of fairly 
good quality under moderate conditions. 

'' There was one exception, however ; the plate which re- 
-ceived two coats of boiled oil speedily became spotted with 
rust, and at the end of the year was much corroded. All 
the painted plates became very much darker in colour owing 
to the deposit of soot from the air, but most of this I have 
«ince removed by rinsing the plates under the water-tap. 

"3. In these experiments I painted strips of sheet-iron as 
before ; and when the second coats were all dry and hard 
•each plate was placed in a wide-mouthed glass bottle, and 
the same volume of ordinary tap water was added in each 
•case. The bottles were then placed on a shelf immediately 
below the laboratory bench, so that the open mouths of 
the bottles were about one-eighth of an inch from the under 
«ide of the table ; in this way the entrance of dust was almost 
entirely prevented, and evaporation was greatly checked, but 
there was access of air to the interior of each bottle. 

9 

** In this third series the tests were made in duplicate for 



k 



42 CHEMISTRY OF PIGMENTS. 

the sake of greater accuracy ; the figures given below ir> 
the third column are the mean of two results, and the- 
duplicates agreed very closely with each other in almost 
all cases. 

*' The bottles were now allowed to remain untouched for 
three months. After about seven days several of the plates 
were perceptibly affected ; this was shown by a turbidity in the 
water; as oxidation proceeded a red precipitate of ferric 
oxide, or rust, appeared and slowly subsided to the bottoms 
of the bottles. After three months' exposure the plates were 
removed, and the amount of iron present in the liquid,, 
and the deposit of rust in each bottle, were determined 
by analysis, and the total amounts of ferric oxide obtained 
in each case were calculated to pounds weight of rust per 
1,500 square feet of painted iron surface ; but, of course, this 
is rather under than over the total amount of corrosion, 
as a certain quantity of corroded iron was loosely attached 
to each plate and to the film of paint. The results obtained,, 
and the composition of the paint in each case, are showtt 
in the following table, and it must be understood that these 
paints are the same as those employed (1) on the shallow irort 
dishes, and (2) on the plates which were exposed to the 
weather for twelve months : — 



THE APPLICATION OF PIGMENTS. 



43 




Ked Lead — 

Red Lead 

Raw Linseed Oil 

* A ' Red Lead- 
Red Lead 

Barytes 

Raw Linseed Oil 

* B ' Red Lead- 
Red Lead 

Barytes 

Raw Linseed Oil 

Orange Lead — 

Orange Lead 

Raw Linseed Oil 

Vermilionette * — 

Barytes 

Vermilionette 

Raw Linseed Oil 

Scarlet Red 2— 

Scarlet Red 

Raw Linseed Oil 

Pure Zinc White — 

Zinc White (Zinc Oxide) 

Refined Linseed Oil 

* A ' Zinc White- 
Zinc White 

Barytes 

Refined Linseed Oil 

* C ' Zinc White- 
Zinc White 

Barytes 

Refined Linseed Oil 

White Lead — 

White Lead 

Refined Linseed Oil 

* A ' White Lead- 
White Lead 

Barytes 

Refined Linseed Oil 

Pale Oxide — 

Pale Oxide (ahout 62 per cent. Fe^O^) 

Boiled Linseed Oil 

Lithopone — 

Lithopone (Zinc Sulphide, Zinc Oxide, Barium 
Sulphate) 

Refined Linseed Oil 

* C ' White Lead- 
White Lead 

Barytes 

Refined Linseed Oil 

^ ' Vermilionette ' is a pigment composed of Orange Lead on which has 
been precipitated about 10 per cent of Eosine. 

2 ' Scarlet Red ' is Red Lead on which has been precipitated Aniline 
Scarlet. 



Composition. 

Per Cent. 
88-88 
11-12 


Rust from 

1,500 
Sq. Yards. 


Lb. 
j-None 


4600 
4600 
10-00 


/■None 


2200 
6600 
1200 


/■None 


88-88 
11-12 


[ None 


83-38 
58-80 

7-87 


j-None 


88-88 
11-12 


[■None 


87-30 
12-70 


1 Traces 


46-00 
46-00 
1000 


j- Traces 


27-27 

63-63 

9-10 


Traces 


92-66 
7-44 


)" 


68-78 

40-83 

6-80 


iso 


88-60 
16-40 

■ 


}81 


87-60 
12-60 


}90 


60-62 

4210 

7-88 


^96 



44 



CHEMISTBY OF PIGMENTS. 




' A ' Red— 

Barytes and Calcium Carbonate . 
Ferric Oxide (96 per cent. FegOj) 
Baw Linseed Oil 

♦C'Bed— 

Barytes 

Ferric Oxide (96 per cent. FegOj) 
Baw Linseed Oil 

Deep Oxide — 

Ferric Oxide (96 per cent. Fe^O^) 
Baw Linseed Oil 

Middle Oxide — 

Ferric Oxide (94 per cent. FCaOj) 
Baw Linseed Oil 

Extra Bright Oxide — 

Ferric Oxide (90 per cent. FeaO,) 
Boiled Linseed Oil ... . 

Barytes — 

Barytes (Natural Barium Sulphate) . 
Baw Linseed Oil 

Pure Oxide * C '— 

Ferric Oxide (90 per cent. FegOj) 
Boiled Linseed Oil .... 

' C ' Celestial Blue— 

Barytes and Calcium Carbonate . 
Celestial Blue (a form of Prussian Blue) 
Baw Linseed Oil 

* B ' Prussian Blue — 

Prussian Blue 

Barytes 

Baw Linseed Oil 

Pure Middle Chrome Yellow — 

Middle Chrome Yellow 

Baw Linseed Oil 

Pure Baw Sienna — 

Baw Sienna 

Baw Linseed Oil 

Pure Graphite — 

Graphite 

Raw Linseed Oil 

Pure Prussian Blue — 

Prussian Blue 

Baw Linseed Oil 

Pure Indian Red — 

Indian Red (70 per cent. FegOj) . 

Raw Linseed Oil 

• A ' Vandyke Brown — 

Barytes 

Baw Linseed Oil 

♦ B ' Middle Oxide— 

Barytes 

Oxide of Iron 

Baw Linseed Oil 



Composition. 



Per Cent. 
78-80 
8-47 
12-73 

80-67 
7-55 

11-88 

86-89 
18-11 

86-89 
13-11 

82-36 
17-66 

88-00 
1200 

76-30 
23-70 

78-04 

9-74 

12-22 

22-76 
46-62 
31-72 

83-68 
16-42 

74-66 
26-34 

69-66 
30-44 

48-27 
61-73 

82-36 
17-66 

66-00 
13-33 
30-67 

76-22 
12-30 
11-48 



Bust from 

1,500 
Sq. Yards. 



Lb. 

118 

123 
123 



1 134 



137 
166 



1 160 



160 

168 

177 
197 
216 
221 
227 

230 
244 



THE APPLICATION OF PIGMENTS. 



45 




Ivory Black — 

Drop Black (Charcoal Black) 

Boiled Oil 

Turkey Red- 
Turkey Red (95 per cent. Fe^O^) . 
Raw Linseed Oil 

' A ' Celestial Blue— 

Baiytes and Calcium Carbonate . 

Celestial Blue 

Raw Linseed Oil 

' B ' Chinese Blue- 
Chinese Blue (another form of Prussian Blue) 

Barytes 

Raw Linseed Oil 

•A' Italian Ochre Paint- 
Italian Ochre 

Barytes 

Raw Linseed Oil 

* A ' Middle Brunswick Green ^ — 

Barytes and Calcium Cajrbonate . 

Superior Middle Brunswick Green 

Raw Linseed Oil 

'C Middle Green— 

Barytes 

Superior Brunswick Green .... 

Raw Linseed Oil 

Superior Yellow — 

Barytes and Calcium Carbonate . 

Chromate of Lead 

Umber 

Raw Linseed Oil 

English Umber — 

English Umber 

Raw Linseed Oil 

' A ' Black— 

Barytes and Calcium Carbonate 

Carbon Black 

Manganese Dioxide 

Boiled Linseed Oil 

Burnt Turkey Umber — 

Burnt Turkey Umber . . 

Raw Linseed Oil 

• C ' Yellow— 

Barytes and Calcium Carbonate 

Chromate of Lead 

Raw Umber 

Raw Linseed Oil 

•C Black— 

Barytes and Calcium Carbonate 

Carbon Black 

Manganese Dioxide 

Raw Linseed Oil 



Bast from 

1.500 
^. Yards. 



Per Cent 
6000 
40-00 

81-16 
18-84 

80-56 

11-83 

7-61 

22-76 
45-52 
31-72 

38-74 
19-00 
42-26 

69-99 
18-24 
11-77 . 

78-32 

9-79 

11-89 

6307 

22-51 

3-31 

11-11 

67-51 
42-49 

68-99 

8-42 

2-46 
2013 

59-20 
40-80 

79-28 

8-31 

1-72 
10-69 

79-30 

4-35 

1-30 
15-05 



} 



Lb. 
250 



}262 



266 



j|275 



296 



.309 



.322 



326 



} 



} 



336 



352 



353 



-369 



392 



^ A mixture of Lead Chromate and Prussian Blue. 



46 



CHEMISTRY OF PIGMENTS. 



Paint. 



Middle Purple Brown — 

Barytes and Calcium Carbonate 

Oxide of Iron 

Raw Linseed Oil . 
• A ' Ultramarine — 

Ultramarine 

Barytes .... 

Raw Linseed Oil . 
Burnt Sienna — 

Burnt Sienna 

Raw Linseed Oil . 
Chinese Blue — 

Chinese Blue 

Raw Linseed Oil , 
Boiled Linseed Oil — 

Boiled Linseed Oil 
Raw Turkey Umber — 

Raw Turkey Umber . 

Raw Linseed Oil . 



Composition. 



Per Gent. 
66-62 
2703 
10-46 

52-63 
26-32 
21-05 

5600 
64-00 

48-27 
51-73 



51-86 
48-15 



Bust from 

1,500 
Sq. Yards. 



Lb. 

1-398 

) 



) 



425 

1 439 

1 441 
600 



-510 



** I think that these three series of experiments, carried out 
under such widely different conditions, and yet yielding such 
similar results, go to show that red or orange lead form the 
best basis for paint pigments amongst those which are in 
every-day use for iron work, especially in situations where 
excessive moisture is likely to be met with. 

** At the same time it must be said that, owing to the 
vigorous chemical action set up in such paints, it is necessary 
that the mixing process shall immediately precede the actual 
painting. 

** Eed-lead paints have not quite the same degree of firm- 
ness as a good oxide of iron paint, which will withstand a great 
amount of rough usage when once it is perfectly dry, and 
this tough and elastic coating yielded by genuine oxide of 
iron paints has much to do with their undoubted popularity 
for outdoor work ; the colour also is far more pleasing to the 
eye than the crude, harsh tone possessed by red lead paints. 

** Zinc oxide appears to have a very high protective value 
as a pigment for use on iron, and stands better in this respect 



THE APPLICATION OF PIGMENTS. 47 

than white lead; also, zinc-white paint, when pure, has a 
good body and covering power, and has the great advantage 
of being non-poisonous to the workers. 

**In a somewhat similar, but less severe, series of trials 
made in 1897, I got a better result with graphite paint than 
in these experiments. A pure graphite paint was used and 
the result showed more corrosion than with pure zinc-oxide 
paint, but less corrosion than with pure oxide of iron paint ; 
red-lead paints in these experiments also gave the best results, 
and still show no rust after two years' immersion. 

'* It is interesting to note the effect produced by the inert 
pigments, barytes and Paris white. I believe the best 
treatment for iron structures is to give them one or two 
■coats of genuine red-lead paint — freshly ground ; and I would 
follow this up with at least two coats of either a genuine 
oxide of iron paint, or, in some cases, of zinc-white paint 
made from pure zinc oxide and genuine linseed oil." 

These experiments of Mr. Smith's are extremely interesting 
and, as he says, certainly show very definitely the marked 
superiority of red lead and zinc white over most other pig- 
ments. White lead ^ occupies a high place on the list, as do 
most of the iron-oxide pigments. The amount of difference 
of action in the case of barytes and raw linseed oil and boiled 
Unseed oil alone is remarkable ; it is not easy to see why so 
inert a substance as barium sulphate should have any other 
than the merest mechanical action on oil ; the difference is 
probably due to either the mechanical formation of a cement 
more impervious than a layer of oxidised oil alone, or 
to raw oil drying more slowly than boiled oil, forming 
a tougher coating less liable to crack and allow erosion to 
commence. The differences between Prussian blue alone 
and diluted with barytes, and Chinese blue alone and 

^ Mr. Smith in a private communication to one of us describes the white 
lead as made by the Dutch process. 



48 CHEMISTRY OF PIGMENTS. 

similarly diluted, in each case with raw oil, suggest that the 
Chinese blue was not washed very free from alkaline salta 
in its preparation, or possibly contained traces of free acid 
or bleaching powder, which is sometimes used for oxidation. 
Some other differences, as those between raw and burnt 
sienna, are very remarkable, and in our opinion, havings 
regard to the fact that **the duplicates agreed very closely 
with each other in almost all cases," the question of soluble 
impurity will be found to have a very important bearing on 
the preservative powers of pigments. 

It is worthy of note that the materials which stand highest 
on Mr. Smith's list, the red and orange lead, zinc white and 
white lead, are all likely to have a considerable chemical 
action on oil, red lead having probably both an oxidising" 
and hydrolysing action, and zinc white and white lead both 
being likely substances to saponify linseed oil, in each case 
of course only to a very slight extent. The inferiority of 
pure carbonate of lead to ordinary white lead (a mixture of 
carbonate and hydroxide) is well known. The following^ 
remarks of Prof. Church illustrate this : ** I tried com- 
parative experiments with . . . pure lead carbonate and the 
Dutch-made lead hydrated carbonate, or ordinary flake white. 
The two lead pigments were washed thoroughly with dis- 
tilled water, and dried before being ground in linseed oil. 
The oil-paints thus prepared were spread in duplicate series 
upon glass, paper and primed canvas. One set was kept in 
a dark box ; the other was exposed to strong light. So- 
decided was the superiority of the ordinary flake white over 
the pure carbonate, when both series of specimens were 
examined after the lapse of various intervals of time, that 
I was reluctantly compelled to abandon my recommendation 
of the latter. Ease in working, solidity of body and rapidity 
of drying were not the only points of superiority, for the films 
of paint, after having been kept a year, showed differences 



THE APPLICATION OF PIGMENTS. 



49 



in hardness and in smoothness of surface, which were all 
in favour of the hydrated carbonate. No discoloration was 
observed in the specimens exposed to light, except in the 
case of the pair upon paper ; the absorbent ground had 
withdrawn some of the protecting oil, and both specimens 
had equally darkened. In darkness all the specimens had 
become of a somewhat greyish yellow, the discoloration 
being about equal in all the pairs, the pair spread on paper 
having, as in the previous case, become darker than the 
others."! 

II METHODS OF APPLICATION OF PIGMENTS. 

In the following table the authors have included most of 
the better-known methods of applying colours to recipient 
surfaces, and have indicated for each method the medium 
used and the surfaces on which it can be suitably employed, 
together with the purposes, as distinguished in the preceding 
part of this chapter, for which the method is used, namely : — 

(a) Artistic (depictive) uses. 

(b) Decorative uses. 

(c) Protective uses. 



Method. 


Medium. 


Purposes 
Used for. 


Surface on which Used. 


Crayon, Pastel . 


Chalk and Gum 


a 


Prepared (usually backed) 




used solid 




Paper 


Water Colour 


Water with Gum, 
etc., and Gly- 


a 


Pure sized Paper 




cerine 






Tempera . . . 


Albuminous or 


a, b 


Prepared Wood, Canvas, 




Gelatinous 




Plaster 




Matter 






Fresco (and Secco) 


Lime Water, Ba- 
ryta Water, 
Water Glass 


a, b 


Prepared Plaster 


Bnoaustic . . . 


Wax 


a 


Wood 



' Chemistry of Paints and Painting, p. 271. 

4 




50 



OHEMISTET OF PIGMENTS. 



Method. 


Medium. 


Purposes 
Used for. 


« 

Surface on which Used, 


Oil (oi: varnish) . 


A drying oil, 


a, bj c 


(a) Prepared Wood, Can- 




thinned 




vas, Copper ; {b and c) 


Keramic — 






almost all Sunaces 


1. Pastes . , 


Clay 


b 




2. Glazes . . 


A Glass 


by C 


Porcelain or Earthenware 


3. Majolica,Del- 


An Opaque Tin 


b, c 


Earthenware (an Opaque 


la ftobia . 


Enamel 




Enamel is also used on 


4. Under Glaze 
6. On Glaze 


Ground Coloured 

Glass Paste ap- 

1 plied with Re- 


K 


Glass) 
Porcelain, Earthenware 


•m^ w ^fc^ ^^^» ^fc^^ ^m^^^^t^ ^a^ v 


sinous Medium 






Enamel. . . . 


An easily fusible 


J 

a, 6, c 


Metal (usually Copper for 




Glass or Frit 


• 


a) 


Stained Glass 


Glass 


b 


f 


Painted Glass . 


An Organic Me- 
dium on Glass 


b 


Glass 


Mosaic .... 




b 


Cement 



Pastels and Crayons. 

Crayons proper, as used for drawing, e.g,, the first sketch 
or outhne of an oil painting, or for crayon studies, are usually 
of three colours — black, white and red. The black and red 
are used for outline and shading, the white to heighten lights. 

The gradation of shade in crayon drawings may be made 
either in the same way as in pencil drawing, by hatching, or 
by rubbing the hatching lines together into uniform or 
graduated tints, resembUng washes, either by the finger tips 
or by the use of a ** stump" — a pointed roll of paper or 
leather. 

Fine charcoal, such as is prepared by burning vine twigs, 
is frequently used as a black pigment for such drawings. 

Coloured chalks, crayons or pastels are used in a similar 
manner, so far as the production of graduated or uniform 
tints is concerned, to the black and red chalks. Very 
beautiful soft effects may be produced by the use of soft 
pastels, and by employing a large number of these little 
crayons a great variety of tints are available, so that a fairly 
correct colour effect may be obtained. 



THE APPLICATION OF PIGMENTS. 51 

Pastels are made of colouring materials diluted with a 
white base, which not only gives the required set of tints by 
the use of varying amounts, but brings the pigment into a 
suitably friable condition. 

Each colour is made in a series of graduated tints, usually 
as many as six, from the fullest workable tint to quite a pale 
shade. When fine strokes with a tint not to be found in the 
set of colours are required, fragments of two or more pastels 
may be crushed under a ** muUer " on a glass plate, moistened, 
and then rolled up into small pastels between the fingers, 
and allowed to dry in the sua or before the fire. For such 
mixed tints on larger surfaces streaks of two or more pastels 
may be rubbed together by the finger in a homogeneous or 
graduated whole like a '*wash'* in water colour or a 
'* softened " part of an oil painting. 

One point about pastels to be remembered is that they 
are fragile ; it is very easy to break them. The angles thus 
produced are extremely useful for giving fine touches, and 
the fragments can be made use of for rubbing in large sur- 
faces of colour. In addition to these accidental sharp edges, 
the usual methods of cutting and grinding on glass paper may 
be adopted. 

It is not possible by the use of such a method — the appli- 
cation of a diluted pigment to a white or only slightly tinted 
surface in isolated particles, not bound together by any dense 
medium causing much internal reflection — to obtain the rich 
full colours of an oil painting. Such drawings or paintings 
must, from the enormous amount of white light reflected, 
always have a weak unsaturated appearance, but for por- 
traiture, especially female heads, certain kinds of landscape 
and flower painting, pastel drawing may b6 used with con- 
siderable success^ 

The following soft pastel crayons of French manufacture 
have been qualitatively examined by us : — 



- 52 



CHEMISTRY OF PIGMENTS. 



Colour. 



A Rosy Scarlet . 

Pale Brick Bed 

Brownish Bed . 

Black to Whitish ( 
Grey , , . j 



Blue . 



• • 



Purple 



Yellow 



Salmon Pink . 



Green 



Crimson . 



Pale Beddish Brown -I 
White 



• • • 



Brown Yellow (Oohre) 






1 

2 
3 
4 
5 

1 

2 

1 
2 
3 
4 
1 
2 
3 
4 
1 
2 
3 
4 
5 
1 
2 
3 
4 
1 
2 
3 
4 
1 
2 
3 
1 
2 
3 
4 
5 
1 
2 
3 
4 
1 
2 
3 



1 
2 
3 
4 






Composition. 



8-7 
3-4 
30 
2.2 
2-2 

3-9 
2-6 

2-1 
2-1 
2-5 
2-8 
1-2 
1-6 
1-9 
2-0 
1-7 
1-9 
20 
2-0 
2-0 
1-06 
1-5 
1-9 
20 
2-7 
2-6 
2-2 
2-1 
3-6 
3-5 
2-9 
8-2 
3-3 
2-8 
2-8 
21 
1-6 
1-7 
1-8 
1-9 
2-4 
21 
2-2 
2-9 

2-8 
3-6 
2-6 
2-2 



Pigment. 



Eosin and Bed 
Lead 

}A Ferric Oxide pig- 
ment with Bed 
Lead 
^Do. do. do. 
The amount of Bed 
Lead greater in 
the lighter tints 

Bone or Ivory Black 



Prussian Blue 



.Cochineal and Ul- 
tramarine 



Lead Chromate 



Bed Lead 



Brunswick Green 
(Prussian Blue & 
Chrome Yellow) 



A Carmine Lake 



}A Peroxide of Lead 
and Oxide of Iron 

White Lead and Calcium Carbonate 



Ferric Hydroxide 



White Base. 



Calcium Carbonate 



Calcium Carbonate 



Calcium Carbonate 



Calcium Carbonate 



Calcium Carbonate 



Calcium Carbonate 



Calcium Carbonate 



Calcium Carbonate 



(1 Apparently undiluted) 
Calcium Carbonate 



Calcium Carbonate 



{•White Lead 

> Calcium Carbonate 



THE APPLICATION OP PIGMENTS. 63 

The use of eosin in colours intended for permanent work 
is certainly not to be recommended. The other colours, with 
the exception of the violet and crimson, might reasonably be 
expected to be highly permanent except, in some cases, in a 
sulphuretted hydrogen atmosphere. 

The determinations of the ** apparent specific gravity " 
given in the above table are useful as indicating the relative 
proportions of colour and base, and were found very useful 
in directing the qualitative examination.^ 

The fullest crimson appeared to be an undiluted lake. 

A quantitative analysis was made of the palest tint of 
blue, which had the following composition: — 

Prussian blue 10*7 

Calcium carbonate 78*0 

Alumina 2*0 

Other matters soluble in acid 0*6 

Insoluble siliceous matter 8*7 

100-0 

As the qualitative examination had indicated, the base 
was almost entirely carbonate of lime — probably a mixture 
of prepared chalk and china clay. 

Water Colour. 

This, in its generally recognised form, purely modern 
method of painting, in which our countrymen have so greatly 
excelled, is essentially a staining process. The colours, ground 
in water, with a suitable gummy medium are applied to the 
surface, a pure sized paper, in thin washes, the high lights 
being left uncovered, or only thinly washed with the appro- 
priate colour ; the darker parts are treated with denser washes, 
or two or more washes are applied until the desired colour 
is obtained. Very beautiful atmospheric effects are produced 
by this means, and good water-colour paintings have a light 

^ The apparent specific gravity of chalk (CaCOj) as used for blackboard 
drawing is 1*30« 



54 CHEMISTRY OF PIGMENTS. 

effect, which is not usually seen in oil paintings, owing to 
the reflected light containing a very much larger proportion 
of white light, as has been stated in the previous chapter. 
The rough surface paper often used contributes greatly to 
this result. It is not always that this peculiarity of water 
colour contributes to artistic effect. For interiors and most 
pictures where richness of colour- is desirable oil is a more 
suitable medium. Nevertheless, a comparison of the tinted 
drawings of the early water colourists, pleasing as they are, 
with the more mature efforts of recognised masters, will 
show what can be done by this method in the way of colour 
imitation (not mere suggestion). There is one thing about 
water colour : it is impossible to reduce or paint out work 
which is too heavy, or requires other alteration. A method 
of obtaining small streaks of high lights, which seems to 
be regarded by masters as legitimate, is to scratch the already 
tinted surface of the paper with a knife, and so expose a 
fresh white surface. 

Many modern works painted with colour ground in an 
aqueous medium are rather paintings in body colour than 
pure water colour. Of this type we may instance an imitation 
of one of the Chantry pictures (which may not be copied 
in oils), which was exposed for sale in London some few 
years ago. This, it is fair to state, was in avowed imitation 
of oils, but many works called water colours are painted 
more or less in this rather unsuitable manner — a sort of 
revival of tempera. 

A report on the permanence of water colours by Dr. W. 
J. Eussell and Captain Abney has already been alluded to at 
some length. Paintings by this method must of necessity be 
more susceptible to atmospheric influences than works in 
which the colour is imbedded in some protective material (as 
varnish) which, itself inert, more or less effectually precludes 
the access of moisture or air. 



THE APPLICATION OF PIGMENTS. 55 

Tempera Painting. 

This ancient method of painting appears to have been 
practised from very early times, but is not much used now for 
artistic purposes. That its capabilities were great is shown 
by the beautiful specimens we still possess of pictures painted 
by this method, which have not only retained all their beauty 
of colour, but in which effect has been obtained in a masterly 
manner. For artistic purposes, however, it is not difficult 
to see why it has been supplanted by the more convenient 
methods of oil and water-colour painting. Tempera, or dis- 
temper painting, is, to describe it briefly, water-colour painting 
in body colour. The surface employed was usually wood, 
sometimes hnen stretched on wood, occasionally plaster. In 
the case of wood (or linen) the suitably smoothed surface was 
primed with whitening applied in a suitable aqueous medium 
(this prepared surface was called gesso) and the colours to be 
used in the picture applied in a similar medium to this surface 
when it had dried. The media of the early Byzantine school 
were very unsatisfactory in that they were far from colour- 
less ; honey, glue and such sticky substances were used by 
them, but Giotto, one of the early Florentines before alluded 
to in this chapter, appears to have introduced a less coloured 
medium, probably white of egg or white and yolk. With 
this more satisfactory medium, or with pale sizes and fish 
glues, tints could be prepared of much greater purity and 
more approximating to those obtained by the painters of 
classical antiquity. Considerable care must have been re- 
quired in this method of painting to avoid, in applying colour 
to parts already partly painted, any stirring up of the former 
tint ; it would seem that the application of washes to modify 
tint, as in water colour, or of glazing or painting over a sur- 
face with thin layers of transparent colour, as in oil painting, 
must have been extremely difficult with a method in which 



56 CHEMISTRY OF PIGMENTS. 

the whole picture and the gesso could be washed off the 
surface. Be this as it may, the process in the hands of 
masters has proved most satisfactory, if it may be judged 
in the usual way, by its results ; in fact, from some attempts 
made by ourselves we think the manipulative weaknesses of 
the method are more apparent than real. 

The finished tempera painting being a very delicate and, 
for reasons discussed in the previous chapter, a somewhat 
weak and chalky-looking production, was treated in many 
cases with a coat of linseed oil or other varnish, which not only 
acted as a preservative, but imparted considerable brilliance 
to the picture. 

From the standpoint of permanency, the principal objec- 
tions to this method of working are : (1) the putrescible nature 
of the medium; (2) its hygroscopic nature, rendering the 
surface liable to considerable expansion and contraction in 
a moist atmosphere, and, therefore, to cracking and scaling ; 
and (3) the chemical nature of the medium, which, containing 
sulphur, is likely on the least putrefaction to evolve sulphu- 
retted hydrogen, and cause blackening of some mineral 
colours. All these objections are much reduced when varnish 
has been applied to the painting, as thus it is rendered less 
hygroscopic, and, consequently, less liable to any sort of 
chemical change, and is also rendered much more tough and 
tenacious. In the dry pure air of Italy tempera paintings 
have preserved their beauty for centuries, and it is to be 
hoped that, under glass in a gallery of fairly uniform tem- 
perature, those specimens which are in our public collections 
may, as things of beauty, be joys for ever ! 

Fresco (Italian, Fresh). 

This favourite style of mural painting (for which it is 
particularly well adapted) is also a most ancient one, having 
been used by the Egyptians, Greeks and Eomans. Anton 



THE APPLICATION OF PIGMENTS. 57 

Mengs, an artist and writer of the eighteenth century, 
expressed his conviction, after having passed the winter of 
1772-73 at Naples, that the mural paintings at Pompeii and 
Herculaneum were executed in the method " biwn fresco ". 
More recent scientific investigations confirm the correctness of 
this decision. These paintings, some 1,800 years old, having 
survived many vicissitudes, present abundant testimony to 
the permanence and suitabiUty of this method for mural 
painting. 

Btum fresco is so called in distinction from secco, a less 
satisfactory method of working ; in the former method the 
painting is performed on the wet ground or intonacoy as it is 
called, in the latter the receptive surface is allowed to dry, 
hence the term secco. 

The wall to be adorned in fresco should be dry and well 
built, and as far as may be free from vibration. It is first 
well damped with water, preferably free from any saUne 
matter other than lime salts, and then the coarser plaster 
applied. This should consist of clean, sharp sand, mixed 
with pure lime ^ paste prepared by slaking lime from chalk, 

1 The following analyses of some Italian, Bavarian and English limestones 
which famish a suitable lime for huon fresco may be of interest. They were 
.undertaken by Mr. B. Phillips for Sir G. Eastlake. 



Travertine. 
Carbonate of lime . 


. 99-4 


Genoa. 
Carbonate of lime . 


63 


Alumina with a trace 




Carbonate of magnesia . 


36 


of oxide of iron . 


•6 


Earthy matter, oxide \ 








of iron , . l 


1 






Bituminous matter J 






100-0 


100 


brought down from Bavarian Alps 
by the Isar. 

Carbonate of lime • . 80 


Durdham Down, Bristol. 
Carbonate of lime . • 


99-5 


Carbonate of magnesia 


. 20 


Bituminous matter 


•3 




100 


Earthy matter 


•2 



1000 
A limestone containing calcium sulphate should not be used for preparing 
lime for fresco. 




58 CHEMISTRY OF PIGMENTS. 

good limestone or marble, with so much water as will form a 
creamy paste, and then allowing this to stand for, say, two 
months, loosely covered, in order that it may absorb carbon 
dioxide from the air and so become partially carbonated. 
According to Sir H. Davy's researches (confirming a statement 
of Vitruvius) on the paintings at Herculaneum and Pompeii, 
the ground used by the ancients was crushed marble cemented 
by lime paste. Pumice, asbestos fibre, infusorial earth, or 
any permanent binding substance, may be similarly used to 
impart firmness to the lime plaster. Each coat of this is- 
allowed to set before another is applied, and is moistened in 
order to prepare it for the next coat. The final surface, or 
intonaco^ is laid on by the plasterer day by day, only so much 
being applied as can be painted over at a sitting. This final 
coat is, of course, laid very flat, and when it is set the outline 
of the design is marked oflf from a cartoon. The colours- 
mixed with lime water or the lime paste are then applied ; if 
they dry in too quickly that part of the surface should be 
sprayed v^th lime water, which vnll assist in binding them 
to the surface. Most careful precautions are necessary in 
fresco painting, both as to manipulation and the choice of 
colours ; when these are duly observed the work is extremely 
permanent. 

Owing to the alkaline nature of the medium the palette 
of the fresco painter is limited, and it is partly to this fact — 
only the most inert colours being admissible — that fresco 
paintings are so enduring. The following list of suitable 
colours may be of interest : — 

^ The Italians usually applied three coats : the rizzaffato^ or rough coat ; 
the arrickbto^ or sand coat ; and the intonaco, or fine surface. 



THE APPLICATION OF PIGMENTS. 



59 



Bed. 


1 
Yellow. Oreen. 


Blue. 


" All kinds of 


All kinds of Ochres i Terra Verte or 


Ultramarine, real 


Burnt Ochres" 


(H.,C.) 1 Verona Green 


(H.) ; factitious 
(H.) 


(H.) 


Raw Sienna (H.) 


(H.) 
Cobalt Green (H.) 


Burnt Sienna (H.) 


Cadmium Yellow 


Cobalt (H.) 


Oxides of Iron (H.) 


(C.) 
Cobalt Yellow (0.) 


Chrome Green 


Some Ultrama- 


Lake -coloured 


(H.,C.) 


rine & Cobalts 


Burnt Vitriol 




Guignet's Green 


(C.) 


(H.) 


; (C-) 




" All the Iron 






Reds" (C.) 






Some varieties of 


1 




Vermilion (C.) 









(H.) Hess of Munich, an eminent fresco painter of the early nineteenth 
century. 

(C.) Prof. Church. 

Any colour which is altered by caustic alkalies, as Prussian 
blue, gamboge or chrome yellow, is unsuitable. 

The chemistry of the process is tolerably obvious. The 
picture is painted on and becomes fixed in a ground of mixed 
lime and carbonate of lime, which, at the same time drying 
and absorbing carbon dioxide from the air, though mostly 
probably still containing free hme, becomes converted on the 
surface into a hard layer of calcium carbonate. This, being 
only to a very slight degree hygroscopic, and absolutely 
unacted on by any of the constituents of the air (carbon 
dioxide and water — a solution of carbonic acid — would 
slowly dissolve it, but this would only occur in the open air 
or in very badly constructed rooms), not only remains intact, 
but is, by suitable means, easily cleaned when exposure to a 
smoky or dust-laden atmosphere has impaired its pristine 
freshness. 

Owing to the nature of the surface and the limited palette 
at his disposal, the works of the fresco painter have usually 
a somewhat sombre effect, this in London being usually 
heightened in a short time by a surface film of carbona- 
ceous matter. Still, for important historical works and 




60 CHEMISTBY OF PIGMENTS. 

mural decoration generally buon fresco is a most suitable 
process. 

Vasari {Lives of the Painters) states of buon fresco that it is 
*' truly the most virile, most sure, most resolute and durable 
of all modes **. 

Btum fresco, from its durable nature, possesses the advan- 
tage of being easily and safely cleaned. Bread, water and a 
sponge, wine (white?), and, it is said, vinegar^ (!) may be 
used. Frescoes on unsuitable walls can also be transferred by 
glueing cloth to them and stripping off cloth and colour and 
re-transferring to another cloth. This apparently very heroic 
method has been used with considerable success ; some 
transferred frescoes may be seen in our National Gallery. 

Secco, or painting on an already dried but re-damped 
plaster ground, in colours mixed with lime water, is, as the 
picture is only on and not in the receptive surface, less 
suitable for serious artistic work ; it was, however, to some 
extent used by the old masters. 

Encaustic Painting. 

This very ancient method of painting is chiefly of interest 
on account of its antiquity. From the very few details and 
very few specimens we possess of such work it would appear 
that colours mixed with wax were applied hot to the receptive 
surface — probably primed with a mixture of wax and white 
— on which the design had been traced with a point, and the 
colour masses were softened by local applications of heated 
tools. The method, though apparently eminently unsuitable 
for very artistic work, certainly had its advantages so far as 
permanence is concerned, as a comparison of the encaustic 
and the tempera painting brought by Mr. Flinders Petrie 
from Egypt will show. 

^ It seems obvious that any acid liquid is undesirable. 



THE APPLICATION OF PIGMENTS. 61 

Oil-Colour Painting. 

Though for decorative purposes colours ground in '* drying'* 
oils have been used from relatively early times, the* adoption 
of an oil or varnish medium as a colour vehicle in artistic 
painting is usually attributed to the brothers Van Eyck, of 
whom it appears that the elder, Hubert, was born in 1366 
and John or Jan in 1390 ; though the latter is more commonly 
credited with the discovery, it seems that Hubert was also a 
master of this development of the art, as a great part of their 
masterpiece (in oils), the ** Adoration of the Lamb" at St. 
Bavon's, Ghent, is known to be painted by him. Be this as 
it may, it is certain that to these great brothers artists are 
greatly indebted, at any rate, for very great improvements in 
this method of painting, improvements which fitted it for 
the finest artistic work, as an examination of the picture 
" Jean Arnolfini and His Wife " by Jan will show. Of the 
Florentine painters Antonio Pollaiuolo was one of the first to 
adopt this medium. An example of this painter's work in 
oils is to be found in the National Gallery, ** The Martyrdom 
of St. Sebastian " (No. 292). 

The works of these early painters in oils, especially those 
of Van Eyck, were executed, it is evident, in a manner some- 
what different to that practised by many modem artists. 
The three pictures by Van Eyck in the National Gallery 
(Nob. 186, 290 and 292) are remarkable for the flatness of 
the surface ; they are all on panels, and though in the cele- 
brated " Jean Arnolfini *' (No. 186) some very clever effects, 
e.g., the mirror, the chandelier and the crystal rosary, are 
produced, these are entirely due to colour, not at all to 
raised surface (of the put-on- with-a-palette-knife kind). On 
looking at the pictures very obliquely the differences in 
level of the outlines of objects are perceptible to a sUght 
extent only. The surfaces in each case are covered with 




62 CHEMISTRY OF PIGMENTS. 

minute cracks, especially where blackish brown (bitumen?) 
and green (Prof. Church suggests verdigris) have been 
used ; there is also some evidence of a repair on the mirror 
in No. 186, but this looks more like the results of an acci- 
dent than the effects of time. These pictures of Van 
Eyck were probably painted with a slower drying medium 
than oil and turpentine ; perhaps a transparent balsam or 
gum resin entered largely into its composition. The exquisite 
finish is not, as Prof. Church well says, compatible with hurry. 
These pictures, No. 186 to a less extent than the others, 
have a rather highly varnished though not exactly shiny 
appearance, due probably to the peculiarity of the medium. 
The painting by PoUaiuoli is very large (9' 6" h. x 6' 7^" w.), 
is considered to be his most important and characteristic 
work and is painted in a much bolder style than Van Eyck's 
careful work ; the colour surfaces are much more defined 
and the differences in level more noticeable ; still there is no 
evidence of any attempt to obtain effect by loading parts of 
the surface with clots of colour ; the differences in level are 
merely due to the use of different colours with different 
proportions of medium, and perhaps painted over more in 
some cases than others and consequently drying down 
differently. The blackish parts of this picture have become 
very blotchy and the whole picture is covered with minute 
cracks and some long ones, which latter have either not 
parted or have been satisfactorily repaired. The picture at 
close quarters presents a rather " sticky " appearance, due 
either to a varnishy medium or a liberal use of varnish after 
finishing : it is well preserved and still a fine bright picture. 
Oil paintings are usually executed on prepared wooden 
panels or stretched canvas, in the case of less important 
pictures on prepared millboard, sometimes, as in the case of 
mural paintings after this method, on a prepared secco or 
dry plaster. Wood appears to have been the favourite surface 



THE APPLICATION OF PIGMENTS. 63 

for small works in early times, and wood was particularly 
suitable to the delicate work of so many early masters. 
Panels should be of well-seasoned wood which has been cut 
up some time before it is finally planed and glass-papered, so 
that both back and front surface may be equally dry and 
seasoned. It is recommended by some ancient authorities 
that the wood should now be boiled. Prof. Church sug- 
gests soaking in water raised to 50° C, and then steaming ; 
by this means soluble matters are extracted and albuminoids 
precipitated. When dry he recommends a wash on both sides 
of corrosive sublimate (we suppose very dilute — say 1-1,000) 
in methylated spirit. After this treatment, which renders it 
unfit for the growth of any organisms, the panel is dried in 
a warm-air chamber for some time, re-glass-papered and 
primed with white lead, copal varnish, and boiled oil (pre- 
pared in manganese salts, not lead). When this coat is quite 
dry another coat in the transverse direction is applied. Then 
coats of oil and white lead alone, and, finally, zinc white and 
drying oil. Each coat is allowed to dry hard, and is rubbed 
down with pumice powder before another is applied. Both 
sides should be treated ahke to prevent warping owing to 
exposure of the back, but of course the rubbing with pumice 
stone is not necessary for the back. When compound panels 
were used by the old painters linen cloth, or less frequently 
parchment, vellum or tinfoil, was often stretched over them 
to receive the colour, and also, of course, the gesso or paint- 
ing ground. Probably the use of a linen surface in this 
manner led to the now almost universal use of canvas 
stretched on a wooden wedged frame for oil painting. The 
following list of surfaces used for oil painting is compiled 
from the catalogue of the National Gallery : — 



64 CHEMISTRY OF PIGMENTS. 



Panels. 


Metal. 


Textile. 


Deal. 


Copper (in many cases). 


Canvas. 


Oak. 


Silver (1). 


Linen. 


Poplar. 




Silk. 


Beech. 




Paper on canvas. 


Chestnut. 




. 



The oil usually used for grinding colours in is pure linseed 
oil ; in the case of badly drying colours, '* boiled " or other 
quick-drying Unseed oil is used. The following oils are also 
used to some extent in artistic work, though for decorative 
and protective purposes the cheaper linseed oil is always 
used. 

Callemantia oil. 

Hemp-seed oil. 

Walnut oil (this is used by artists as less liable to cracking than 

linseed). 
Poppy-seed oil (this is used by artists as less liable to cracking than. 

linseed). 
Niger-seed oil. 

Fir-seed oil (used for varnishes). 
Japanese wood oil (used for varnishes). 

Colours ground in oil are, without dilution of some kind,, 
too stiff, and sometimes too deep coloured for use alone. It 
is, therefore, common to dilute the pigment with a suitable 
white *' base '* to the required shade, and to reduce to a 
workable consistency with some volatile liquid miscible with 
oil. This liquid is usually " oil " or ** spirit " of turpentine, a^ 
tolerably pure mixture of terpenes, with only a small propor- 
tion of oxidised product (resin), but of late years various 
turpentine substitutes, mostly of the nature of petroleum 
spirit, have to some extent come into use. It is also cus- 
tomary with both artists and decorators to use to a greater or 
less extent materials known as " driers," or ** megilp," which,, 
containing compounds of lead or manganese as their active 
constituents, facilitate the oxidation and ** drying " of the 
oily vehicle. 



THE APPLICATION OF PIGMENTS. 66 

A surface having been covered with a coat of paint pre- 
pared as above, two actions at once begin. The turpentine 
or other volatile thinning material evaporates more or less 
rapidly, and while this is going on the oil, especially if drying 
materials have been added, or the colour itself or the white 
diluting material, has high drying properties, becomes more 
viscous, and a film of hardened oxidised oil forms with the 
colour imbedded in it. This film, unless too much driers 
has been used, is tough and durable, and in the space of 
twenty-four hours or more is sufiiciently established for a 
second painting. This convenient property of oil colour is 
of the greatest value to the artist and to the house painter ; 
it enables the former to obtain very fine effects by the 
superimposition of thin ** glazes " of transparent colour, by 
** stippling " and various other artistic devices ; it also enables 
him to make alterations, to heighten lights and to run 
different colours close to one another in one painting in a 
way which is impossible to the water colourist; the house 
painter on his priming or first coat of good tough full-bodied 
paint can apply further protective and final decorative coats, 
the latter in colours which could not themselves be used as 
priming on account of their poor covering power and opacity. 

In mixing paint care should be taken that too much 
thinning material is not used on the one hand, or, on the 
other, an excess of oil. In the former case, the solid particles 
are likely not to remain properly in suspension in the mass 
while it is being applied, and the result is that, though flat, 
the coat is of uneven tint and also dries very dull and 
chalky-looking owing to insufficiency of oil, while an excess 
of oil renders the paint difficult to work, slow drying, or, 
rather, forming only a surface skin with "tacky" paint 
underneath, and altogether unsuitable either for painting 
over or for protective purposes. The aim should be to use 
pigment, oil and turps in such proportions that a smooth 



66 CHEMISTRY OF PIGMENTS. 

layer of pigment, perfectly imbedded in a thoroughly dried 
and resinified layer of oil varnish, is the result. In the case 
of artistic work and frequently in decorative work any de- 
ficiency in this respect is repaired by an application to the 
properly dried work of one or more coats of good transparent 
copal or other varnish. This not only increases the durability 
of the work by firmly cementing the colour particles in filling 
in the interstices caused by shrinking of the oil film, but by 
its high refractive index causes much of the white light which 
would be reflected from the unvarnished picture to be lost by 
internal reflection, and so gives that fuU mellow appearance 
and purity of tint which one associates with a finished oil 
painting. In the case of decorative work varnishing not only 
adds to its appearance, but gives to the paint a much greater 
durability by reason of the waterproof nature of the varnish. 

Keramic Art. 

A very important use of colours is to decorate pottery, 
and for this purpose the colours must be very carefully 
selected and applied in a highly specialised manner. We 
can only most briefly touch on some of the most important 
processes by which keramic ware is decorated. In the first 
place it is obvious that, in view of the high temperature to 
which all pottery is exposed in manufacture, the only colours 
admissible are those which are purely inorganic in their 
nature and which are non-volatile, at least at a red heat. 
Colours may be used in the following ways : — 
L — Coloured pastes. 

II. — Colours on the paste. 

(a) Glazes or transparent coloured glasses. 

(b) Enamels or opaque glasses. 

(c) Underglaze colours. 

(d) On glaze colours. 



THE APPLICATION OP PIGMENTS. 



67 



It will be seen from this classification that two principal 
methods are adopted : the use of a coloured paste, which of 
course is the same colour all through, and the application of 
surface colours. We will consider these methods briefly. 

L — Coloured Pastes, 

All pastes containing fusible as well as plastic materials 
can be beautifully stained by the addition of suitable metallic 
oxides before firing. We give some proportions used in the 
following table : — 



Colour. 

Pale Blue 
Deep Blue 

Green . 
Blue Green 



Colouring Material. 
Oxide of Cobalt 



•{ 



%% 



>> 



»» 



j» 



j» 



tt 



>i 



»» 



Chromium 

>» 
Cobalt . 
Zinc 



Bronze Green Calcined Oxide of Nickel 
Brown . . „ „ Iron 

Yellow . . Oxide of Titanium 

Iron 
Cobalt 



Black 



■{ 



)} 



11 



Parts. 

. 5 

. 10 
. 5 

. 10 

2-5 
. 1-25 
. 1-25 
. 5 

. 15 

. 10 
. 7 
. 8 



Paste to make up 
100 parts in each' 
case. 



Such coloured pastes would be used for mosaic tiles and 
tesserae, coloured porcelain, etc. 

//. — Colours on the Paste, 

(a) Coloured Glazes. — These are applied either by dipping 
or with a large camel-hair brush to the surface of the 
** biscuit " or unglazed pottery. These glazes are largely 
used for coloured glazed tiles and self-coloured ware gener- 
ally. A French glaze given by Salvetat, Dictionnaire des 
Arts et Manufactures, is — 

Red lead 2,000 parts 

Flint 1,000 „ 

Borate of lime 600 „ 

coloured by 40 to 125 parts cobalt oxide for blue, 100 to 500 




68 CHEMISTRY OF PIGMENTS. 

parts copper oxide (CuO) for blue greens, 70 to 200 parts ferric 
oxide for ivory to strong yellow, 70 to 125 parts oxide of. 
manganese (MngOJ for madder- to purple-brown, etc. The 
mixture is coarsely ground, melted, poured out into water 
and ground fine. An English mixture, rather less fusible, 
is made from flint 100, China stone 90, red lead 360, borax 
40 parts, coloured similarly to the above. 

A very lovely turquoise blue frit used by the Egyptians 
and Assyrians was examined by Sir H. Davy, who found it 
to be a frit of soda, silica and cupric oxide in the proportions : 
carbonate of soda 15, silica 20, copper 3. Vitruvius says it 
was made by mixing copper filings, alkali and finely ground 
sand, making into balls with water and fusing in a glass 
furnace. Salvetat gives the following : — 





Body. 




Gl&ze (fritted). 




Silica . 


• • • 


93-0 


Sand 


900 


Alumina 


• • • 


4-0 


Sodium bicarbonate . 


400 


Lime . 


• • • 


20 


Chalk 


100 


Potash 


• • • 


0-6 


Cupric oxide 


135 



(6) Enamels. -^These semi- vitrified, opaque materials are 
really stanniferous glazes — glazes made opaque by reason of 
their containing oxide of tin. Majolica and Delia Bobbia wares 
were decorated with such enamels. A revival of this kind 
of decoration has set in during this century, but, judging 
from the precautions taken in the winter for protecting the 
celebrated majoUca fountain of the 1851 Exhibition, now 
outside the Bethnal Green Museum, the majoUca of to-day 
is not a very suitable material for outdoor work in a variable 
and damp climate. A few enamels by Deck are taken, as are 
most of the recipes in this section, from the article " Pottery," 
in Thorpe's Dictionary of Applied Chemistry, by Mr. W. Barton. 

J^hite, lead and tin ashes, 44 ; sand, 44 ; soda, 2 ; common salt, 8 ; red 

lead, 2. 
Yellow, white as above, 91 ; oxide of antimony, 9. 



THE APPLICATION OF PIGMENTS. 69 

BltiBy white as above, 95 ; cobalt oxide, 5. 

Green, white as above, 95 ; cuprio oxide, 5. 

Yellow-green, white as above, 94 ; cupric oxide, 4 ; antimoniate of lead, 2. 

Violet, white as above, 96 ; manganese dioxide, 4. 

(c) Underglaze Golov/rs. — Colours used for painting on the 
biscuit, which is subsequently glazed, must, when mixed with 
their silicious base, be sufiSciently infusible and insoluble in 
the glaze to remain under (and protected by) it, and not to 
run into it, and must also be of such a nature as to hold to 
the glaze and not cause it to chip or crack. Underglaze 
colouring is the most satisfactory way of applying colours 
locally to porcelain or other keramic ware which is intended 
for use. We give some mixtures (from the article referred 
to):— 

Black. — Eight parts native chromate of iron, 3 parts of 
MugO^, 3 parts of CoO, 1 part of flint ; calcined together 
strongly, and then ground fine. 

Dark Blue. — Four parts of CoO, 1 part of flint, 1 part of 
chalk ; ground together. 

Azure Blue, — Sixty parts of ammonium alum, 3 parts of 
CoO ; calcined strongly, then ground and washed thoroughly 
till free from traces of acid. 

Blue-Green. — Twelve parts of borax, 12 parts of chalk, 12 
parts of oxide of zinc, 24 parts of green oxide of chromium, 4 
parts of oxide of cobalt ; calcine well together and grind till fine. 

Dark Brown. — Eight parts of native chromate of iron, 4 
parts of oxide of zinc, 2 parts of oxide of iron ; ground well 
together, calcined strongly and re-ground. 

Bed'Brovm. — Six parts of precipitated chromate of iron, 
20 parts of oxide of zinc, 3 parts of litharge; calcine together 
strongly, and then grind till fine. 

Pink Colour. — One hundred parts oxide of tin, 34 parts 
chalk, 1 part oxide of chromium, 6 parts silica ; mixed well 
together, calcined strongly and ground. 



i 



70 CHEMISTRY OF PIGMENTS. 

Yellow. — Three parts oxide of antimony, 6 parts red lead, 
2 parts flint, 1 part oxide of tin ; calcined together and then 
ground. 

In all these colours great importance is to be attached to 
the grinding of the ingredients before, and the colour after, 
calcining. 

(d) On Glaze Colours, — These colours are really fusible 
glasses, which, when applied to the glazed surface of the 
article (usually painted or printed with a resinous medium 
or thick boiled oil) and raised to a red heat, adhere before 
the glaze itself is remelted. They are by no means entirely 
satisfactory ; unless the coefficients of expansion of glaze 
and colour are almost equal, the colour is liable to crack and 
sphnter. Work done in this way is less brilliant-looking 
and less artistic than underglaze work, besides being less 
permanent. 

These colours are divided into two classes, regular kiln 
colours and hard kiln colours, according to the temperature 
of firing, the latter requiring the higher temperature. The 
composition of several fluxes, both Continental and Stafford- 
shire, are given in the article in Thorpe's Dictionary, as also 
are several colours, including, in addition to the colouring 
materials already mentioned, oxides of uranium (black and 
yellow), antimoniate of potash, purple of Cassius (finely 
divided reduced gold), silver and oxide of gold. 

The above brief outline of the methods of colouring 
keramic ware, and of the preparation and nature of the 
colours available for this purpose, will serve to indicate to 
some extent the requirements and scope of this kind of work. 
It is unnecessary to dilate on the extreme permanence which 
may be expected of suitable colours suitably applied to such 
durable materials, especially when either diffused through 
the entire mass, or in or under the glaze or enamel. 



THE APPLICATION OF PIGMENTS. 71 

Enamel. 

This method of applying colours, though strictly including 
the various methods of glazing and painting on keramic ware, 
is, in its restricted sense, the decoration or protection of 
metals by means of a coating of glaze which may or may 
not be used as the surface for further decoration. 

Enamel painting, a method but little practised by artists 
on account of its difficulties and uncertainties, is really paint- 
ing on enamel ; a metal plate, usually copper, in some cases 
gold, is annealed and then covered with white enamel powder 
on both sides, the powder being an easily fusible glass with 
stannic or arsenious oxide or calcium phosphate suspended 
in it. This is then fired, cooled, and the coat of enamel 
which is formed ground smooth, a further coat is then burnt 
on the face to be painted, and a more fusible transparent flux 
then burnt on and ground. The painting is done with 
powdered coloured ** frits," or glasses, in suitable media, and 
each colour burnt in separately. It will be seen that most 
subjects would require several paintings and firings. When 
it is considered that each of these operations is likely to result 
in failure, either through an inappropriate shade being burnt 
in, for the colour is only properly developed by firing, or by 
cracking in cooling, which, in the case of a large plate, is a 
serious risk, it will be understood that the art is but Uttle 
practised. 

Cloisonne is a method of decorating copper and other 
metal vessels in which the design is traced on the metal, 
and the different parts which should take different colours 
separated by strips of metal, or wires, fastened to the surface 
(by brazing). The low level surfaces thus formed are filled 
with enamel, and the whole is then fired, and when cold the 
surface ground smooth. The colours are in this kind of 
work separated by metal bands, or fillets, which show, like 



72 CHEMISTRY OF PIGMENTS. 

the leading of a painted window. Another method, champ 
lev^, practised in Germany and at Limoges, a town cele- 
brated for its enamel paintings on convex copper plates in 
grey and white on a blue ground, was to trace the design 
on copper and then cut away the parts to be enamelled with 
a graver, filling in these hollows, firing, and then grinding 
smooth. In this case, as in that of cloisonne, raised metal 
surfaces are visible and must be treated as part of the design. 

Enamel is used largely now on iron for advertising pur- 
poses. Iron sheets enamelled blue and white or other colours 
have largely supplanted the poster for permanent advertise- 
ments and notices. The method of working is similar to that 
for copper. 

In any case it is desirable that the coefficients of expansion 
of metal and enamel should be so adjusted by experiment as 
not to be very different. If this is not the case chipping off 
is likely to occur on cooling. 

The colours used for enamel work are very similar to those 
described as being used for the decoration of keramic ware ; 
a description of many of these is given in the section devoted 
to that branch of art. 

Stained and Painted Glass. 

Glass is, as is well known, a mixture of various silicates 
obtained by fusion and subsequent cooling, this process being 
conducted so (relatively) rapidly that crystallisation does not 
take place, and the resulting product is (usually) transparent. 

Mixtures of the silicates of soda and lime, potash and lime 
and potash and lead are used for the production of coloured 
glass, the colour being imparted by the addition of small 
proportions of various metallic oxides. The student of 
chemistry in a very early period of his career is taught to 
form deductions as to the nature of substances from the 



THE APPLICATION OF PIGMENTS. 73 

•colour imparted by them to *' borax beads ". The borax 
*^* pastes*' thus produced are used in the manufacture of 
Artificial gems for theatrical and other purposes. Speaking 
.generally, the oxides which impart a colour to borax impart 
a. similar colour to glass. We give a list of substances used 
-for colouring glass which will indicate the general composi- 
tion of coloured glasses. 

Bliie glasses are produced, the lighter sky-blue colours, by 

the addition of 0*8 to 1*2 per cent, of cupric oxide (CuO); the 

deeper, more violet glasses, by the addition of oxide of cobalt 

<(about 0*15 per cent), or zafiEre (0*35 to 0*4 per cent). A pale 

blue or blue-green glass is produced by partial oxidation of 

..glass coloured by iron. 

Amethyst coloured glass contains 2 to 2*5 per cent, of 

manganese-dioxide (pyrolusite), mixed with about twice that 

-amount of nitre to prevent reduction to the manganous state. 

(This agrees with the behaviour of manganese in borax in 

the oxidising and reducing flames respectively.) 

Yellow glasses are obtained in a variety of ways : by the 
addition of wood or of charcoal, in which case carbon appears 
to be the pigment; by the addition of sulphur (not to lead 
.glass, as this would produce lead sulphide, which is black), 
in which case a yellow alkaline sulphide appears to be pro- 
duced or with manganese dioxide and ferric oxide, or by 
antimoniate of lead (antimoniate of lead is used as a yellow 
pigment by artists under the name of Naples yellow). Uranic 
oxide also produces a fluorescent yellow glass, the appearance 
•of which is pleasing and is well known, somewhat resembling 
'that of an alkahne solution of fluorescein. 

Orange-coloured glass is prepared by using manganese 
•dioxide, and ferric oxide, the ferric oxide being slightly in 
•excess. 

Bed glass is coloured by cuprous oxide, CugO (rose 
copper), in which case great care must be taken to avoid 



74 CHEMISTRY OF PIGMENTS. 

oxidation to cupric oxide with formation of a blue or green 
glass. Metallic iron (1 to 1*5 per cent.) and cupric oxide (about 
1 per cent.) are added, and the mixture is melted and stirred 
with an iron rod. The glass is colourless when taken out 
of the crucible, but turns red on cooling. A more crimson 
glass is obtained by the use of gold, which is added to the 
sand of which the glass is to be made, in the form of chloride.. 
Not more than 0*1 per cent, gold is used, and even less than 
this gives a fine rich ruby red. The colour, like that of the 
purple of Cassius is due to the presence of finely divided gold. 

Green glass is obtained by using a mixture of oxide of iron' 
and oxide of copper, with the addition of nitre to maintain 
these in the higher state of oxidation. Chromium oxide also 
produces a green, as does a mixture of antimonious oxide and 
cobalt. Bottle green is produced by ferrous oxide, iron being 
added as iron filings, and dissolved by the glass to a ferrous 
oxide. 

Black glass is produced by the use of mixtures of oxides 
as cobalt, copper, iron or manganese, one of these being in 
sufficient excess to remain undissolved as dark particles. 

The addition of sulphur (7 to 10 per cent.) by forming 
ferrous sulphide also produces a black glass. This is prepared 
in Bohemia, and is known as hyalithe. 

White glass, opal or translucent glass is prepared either by 
the use of stannic oxide with lead oxide produced by heating 
the metals together ; by arsenious oxide in a lead potash or 
lead potash lime glass, or by calcium phosphate, or by the 
use of fluorides as cryolite or, better, sodium fluoride. 

Aventurine glass contains either finely divided cuprous 
oxide, or finely divided copper. It is, at any rate, a yellow 
glass full of sparkling red metallic-looking particles. It is 
prepared according to Hautefeuille from such mixtures as. 
the following : — 



THE APPLICATION OF PIGMENTS. 75 

Crystal 2,000, saltpetre 200, copper turnings 125, ferric oxide 60 parts. 

Or, 

Sand 1,500, chalk 857, anhydrous carbonate of soda 801, carbonate of 
potash 143, saltpetre 200, copper turnings 125 parts. 

Or, 

White soda glass 1,200, sand 600, carbonate of soda 650, saltpetre 200^ 
copper turnings 125. 

When the glass is liquid, 38 parts of iron filings rolled up 
in paper are thrown into the pot, and the mixture stirred with 
a red-hot iron. The glass becomes blood red, opaque, and 
full of small bubbles, the furnace draught is stopped, the pot 
covered, heaped with ashes and allowed to cool very slowly. 
Next day the crucible is broken, and aventurine found to 
have been produced. It is difiBcult to produce a good article, 
as the product is liable to become streaky, to contain bubbles, 
or the crystals may be too fine. 

Chromium aventwrine was discovered by Pelouze in 1865. 
It is produced by heating sand 250, carbonate of soda 100, 
calc spar 50, bichrome (bichromate presumably) 20 to 40 
parts. The chromium oxide resulting on fusion is in greater 
amount than will dissolve to form a green glass, and this 
excess is suspended in the glass as brilliant green crystals. 

Speaking generally, it is admitted by glass-makers them- 
selves that the glass of to-day, though certainly very superior 
to that of the early and middle part of last century, is 
decidedly inferior to good old glass in richness of tint, and 
probably in weathering qualities. 

Painted glass such as is seen in windows is produced by 
shading and burning in the shades on coloured glass. 
Briefly, the process is this : The design is drawn full size 
from the coloured sketch on white paper in black chalk, or 
(in France) in white on blue paper, the different colours 
being marked on the parts. The coloured glasses are then 



76 CHEMISTRY OF PIGMENTS. 

selected, agreeing as nearly as possible with the brightest parts 
of the respective colours in the coloured sketch, and are cut to 
shape with a diamond, shaded first in water colour, then in 
oil with an oxide of iron paint, a little borax being used as a 
flux. In some cases actual painting with similar colours to 
those used for tinting glass is resorted to. The plates are 
then placed on shelves covered with powdered lime in a 
furnace, which is heated suflSciently to so soften them that 
the shading sinks in and becomes incorporated with the 
glass. Various methods of shading, as smudging, stippling, 
and hatching with lines are adopted ; pieces of high light are, 
where necessary, wiped out of the shading before it is burnt 
in, and in some cases flashed glass (coloured and colourless 
glass welded together) is etched locally with hydrofluoric 
acid until only the colourless glass is left. The process is 
difl&cult and complicated, and the above is only the crudest 
outline. Much modern glass seems to be too soft to with- 
stand the erosive effect of town atmosphere. 

Mosaic. 

Mosaic is a method of decoration in which small coloured 
dice or tesserae imbedded in cement are arranged to form 
a pattern or design. It is, provided the cement is good, an 
absolutely permanent kind of work, as the tesserae are usually 
composed of natural-coloured stones, or of marbles, or of fired 
earthenware. Speaking generally it is rather a method of 
utilising coloured substances for decoration than of applica- 
tion of pigments in the ordinary sense of prepared pigments, 
and needs no more than a passing notice here, though as 
a method of decoration, especially under the trying conditions 
which prevail in modern towns, its importance is very great. 



CHAPTEE III. 

INORGANIC PIGMENTS. 

I.— WHITE PIGMENTS. 

White Lead {Synonyms — Cerussa Alba, Cremnitz White, Flake 

White). 

Of all white pigments this is the most, widely used and most 
important ; it is also one of those most frequently sophisti- 
cated, being sometimes adulterated, and frequently replaced 
by other lead whites. Its great covering power, ease of 
working with oil and permanence in that medium, combined 
with its good drying qualities, render it most suitable both for 
use alone and for diluting other (coloured) pigments. 

It is, we believe, entirely correct to state that none of the 
many artificial white leads or other white compounds of lead 
possess to anything like the same extent the all-round good 
qualities of white lead which has been prepared according to 
the so-called Dutch or stack process ; even in those cases in 
which the chemical composition of the white as shown by 
analysis is correct the physical condition does not appear to 
be so satisfactory. One objection brought against white lead 
(principally by those interested in other whites) is that it is 
more or less blackened by exposure to air contaminated with 
sulphuretted hydrogen. This impeachment, so far as it goes, 
is correct, but under ordinary conditions serious alteration 
does not occur, and, a fact often disregarded, white lead on 



78 CHEMISTRY OF PIGMENTS. 

•exposure to light and pure air recovers in course of time. 
Very old pictures in which white lead has been used often 
exhibit an ivory-like yellowness, owing probably to combina- 
tion with the oil or varnish of the medium, but this yellow 
colour is seldom sufl&cient to spoil an effect, and usually is by 
no means unpleasant. 

This property of white lead, of entering into combination 
with linseed oil, is a most valuable one, as to it is probably 
due in no small degree the toughness and imperviousness of 
the coat obtained. The experiments of a maker of whites, 
quoted by Mr. A. P. Laurie in his Cantor Lectures, in which 
strips of canvas were painted with various whites and allowed 
to flutter in the breeze, and in which it was found that, after 
wind and weather had caused all the other whites to peel and 
crack, the canvas painted with white lead was still well 
coated, are particularly interesting in this connection. 

The most ancient and most satisfactory method of 
preparing white lead is the so-called Dutch process, or stack 
corrosion. In this, lead in the form of coils or gratings is 
stacked up over pots containing dilute acetic acid or vinegar 
and imbedded in fermenting horse dung or spent tan ; sev- 
eral layers of pots are stacked one over the other in large 
brick chambers or sheds capable of holding several tons of 
lead. The temperature of the stack rises considerably as a re- 
sult of the fermentation of the dung or tan, the temperature of 
the mass reaching from 140° F. to 150° F. according to circum- 
stances. Acetic acid vapours and carbon-dioxide are evolved, 
which attack the surface of the lead in the presence of aqueous 
vapour, forming first a film of lead oxide which is gradually 
converted into basic acetate of lead. This, acted on by carbon- 
dioxide, becomes white lead and normal lead acetate. The 
normal acetate and fresh lead oxide re-form basic acetate, 
which is again decomposed and re-formed, the resulting 
compound at the end of some months, when the heating 



INORGANIC PIGMENTS. 79 

-effect has passed off and chemical action ceased, being the 
mixture or compound of lead hydroxide and carbonate known 
as white lead. This forms a thick crust on the surface of 
the, by this time, much corroded lead plates, etc. This is 
detached and ground and levigated in order to obtain the 
requisite degree of fineness. The percentage of lead converted 
•depends on its state of aggregation and on the details of 
^working; it varies from 50 to 70 per cent. Some makers, 
prefer to cast the lead into rather thick coils, stars or 
Ratings, as it is easier to detach the white lead when the 
percentage of corroded lead is low. 

In England tan is usually used, in Holland dung, to 
produce the carbon dioxide and to cause the requisite in- 
crease in temperature ; it is also more common in England 
to use dilute acetic acid from pyroligneous acid rather than 
vinegar, otherwise the processes in general use in the two 
countries are similar. This process of stack corrosion is 
extremely slow, the operation, as has been already stated, 
extending over several months, but the product is, for reasons 
w^hich will be considered below, most satisfactory. 

A process closely allied to the stack process, and which 
may be considered as a bond-fide method of preparing white 
lead, is that used in Germany, originally at Kremsnow, but 
to a greater extent at Klagenfurt. Thin sheets of lead are 
exposed in wooden boxes, heated artificially to about 85° C, 
and submitted to the vapours rising from a mixture of 
wine lees and vinegar spread on the bottom of the boxes. 
A modification of this process consists in suspending the 
sheets of lead in chests or chambers on the floors of which 
are placed vessels of acetic acid. Air and carbon-dioxide are 
passed into these chambers, and in either case the German 
method is more rapid than either English or Dutch. The 
product, however, is not so satisfactory. 

The French or Clichy method is altogether different from 



80 CHEMISTRY OF PIGMENTS. 

either of the above processes. It was devised by the well- 
known chemist, Thenard, and is one of the earliest of the- 
many precipitation processes. Basic acetate of lead is formed 
by digesting litharge (PbO) with acetic acid of 1*056 specific 
gravity. The mixture is kept agitated by a mechanical device, 
and litharge added until the solution has a specific gravity 
of 1*145. The liquor is then run into a settling tank where 
any insoluble matters deposit, and the clear solution is trans- 
ferred to a vessel where it is treated with carbon-dioxide 
prepared by heating a mixture of chalk and coke in a kiln ; 
the kiln gases are drawn off by a fan and forced through a 
scrubber, and then through pipes into the precipitating tank. 
In about twelve or fourteen hours the conversion is as- 
complete as is possible — that is, white lead and normal acetate 
are formed. The latter is pumped off and digested with 
litharge to re-form basic acetate, the first washings of the 
white lead being used again, as they also contain acetate. 
The white lead formed is carefully washed and ground. This- 
process is in some respects very similar to the dry processes,, 
but the product is not so satisfactory as a pigment. 

In Milner's process a basic chloride of lead is produced 
by the interaction of litharge, salt and water. The mixture • 
at the ordinary temperature becomes white and pasty ; a 
considerable evolution of heat occurs, and the solution be- 
comes alkaline owing to the formation of sodium hydroxide. 
The decomposition is usually effected in mills, and the 
proportions used are 1 of salt, 4 of litharge, and 16 of water.. 
The agitation is continued for about three hours (if for & 
shorter period the mass is too pasty), and after this time the 
entire mass is creamy, and can be run out. The carbonatiott 
is effected in an iron lead-lined vessel with hemispherical ends,, 
placed upright. At the top is an opening through which the 
basic chloride mixture is introduced, and another by means- 
of which the pressure is regulated ; an opening near the 



INOBGANIC PIGMENTS. 81 

bottom serves to draw off the white lead and samples which 
are examined from time to time during the conversion. The 
carbon-dioxide is, as in the French process, prepared from 
coke and chalk, and is scrubbed in coke water towers. When 
the action is complete a test sample is no longer alkaline, as 
all the chlorine of the chloride has combined with the sodium 
previously existing as hydroxide, forming common salt ; and 
if shaken in a glass vessel the creamy homogeneous mass 
leaves a frosted appearance on the sides, and in a few minutes 
the white lead has separated out, leaving a clear liquid above, 
and branching patterns on the sides of the vessel which were 
coated. Any further addition of carbon-dioxide causes a de- 
terioration in quality of the product, which becomes granular. 
The white thus obtained is washed free from salt, and though 
inferior to stack lead, is well suited for use as a paint. 

Many other processes, as precipitation from a solution 
of basic nitrate by COg, action of CO2, air and water on finely 
divided lead, action of COg on a paste of litharge and lead 
acetate, have been suggested and made the subject of patents. 
So far, however, none of these have yielded so satisfactory 
a product as that obtained by the older processes, though in 
many cases closely approximating in chemical composition. 

Whatever process may be adopted, if a product at all 

satisfactory be required, it is necessary that very pure lead, 

such as is prepared by the Pattinson or Eogan processes, 

or by a modification of the Parkes zinc process, should be 

used for the preparation of white lead, as the presence of 

even very small quantities of other metals is likely to affect 

the colour of the product. A slight pink tinge, which is 

sometimes observable in corrosions, is said to be due to 

the presence of a suboxide of lead ; others attribute it to 

the presence of minute quantities of silver compounds. The 

tan also, either by touching or by liquid from it falling on 

the deposit, is likely to cause discoloration. It must be 

6 



82 CHEMISTRY OF PIGMENTS. 

remembered that basic acetate of lead is an extremely good 
substance for removing colouring matters from liquids, and 
that any drippings from boards used in stacking are likely 
to give up any trace of yellow or brown colour extracted 
from the wood to the ** corrosion '*. A discoloration, if not 
serious, is sometimes corrected by the addition of a very 
minute quantity of Prussian blue, which gives a bluish tinge, 
and makes the white appear very pure in tone. 

A most important objection to the stack process, or 
indeed to any dry process of preparing white lead, is the 
deleterious effect the very fine dust raised has on the human 
system. This is certainly a serious drawback, and one which 
has in the past called for protective legislation on behalf of 
the work-people, who, in too many instances, require much 
supervision to induce them to take needful precautions. 

We give below in full the special rules prescribed under 
the Factory and Workshop Acts, 1878-91, for observance in 
white-lead works : — 

"Duties of Occupiers. 

** 1. They shall provide respirators, overall suits and head 
coverings, to be worn by the persons employed in the depart- 
ments enumerated below, under ' Duties of Persons 
Employed '. 

" 2. They shall take care that every stack is fitted with a 
standpipe, or movable hose, and an adequate supply of 
water, distributed by a very fine rose or watering can, for 
damping the white bed before stripping. 

**3. They shall see that no female shall be employed 
without a certificate of fitness from a medical man, to be 
obtained within one week from the date of employment. 

" 4. They shall see that no person shall be re-employed 
after absence through illness without a certificate from a 
medical man. 



INORGANIC PIGMENTS. 83 

** 5. They shall provide overalls for females in all blue beds 
v^here the returns are used without being remelted, and 
overalls and head coverings for females in all other parts of 
the works except the casting shops. 

** 6. That the wearing of shoes and stockings be optional, 
but that no females shall be permitted to wear the same shoes 
and stockings in the works as they wear in going to and from 
the place of employment. 

" 7. They shall provide suiBficient bath accommodation for 
all men and womQn employed. 

**8. They shall provide dressing-rooms, a dining-room, 
lavatories, and a cloak-room in which the ordinary clothes of 
all workers are to be kept apart from their working clothes. 

"9. They shall arrange for a weekly visit by a doctor, 
who shall examine every worker individually, and who shall 
enter the result of each examination in the proper register. 

** 10. They shall cause such a register to be kept, and 
shall have entered in it the date when each worker com- 
mences and leaves emplojnnent, and the date when each 
worker takes a bath. 

** 11. They shall cause every case of illness from lead 
poisoning to be reported both to H.M. Inspector of Factories 
for the district, and to the Certifying Surgeon. 

** 12. They shall cause each man or woman to take a bath 
at least once a week, and to wash in the lavatory before 
bathing. 

**13. They shall deliver to the persons employed the 
articles of clothing which are required to be worn, and they 
shall see that they are put on. At the end of every day's 
work they shall collect and have thoroughly washed all those 
which have been used in the stoves, and those which have 
been used in other departments, once a week. 

" 14. They shall see that the general lavatory is thoroughly 
cleansed and supplied with clean towels after every meal. 







84 CHEMISTBY OF PIGMENTS. 

" 15. They shall have the dressing-rooms, baths, and 
w.c.'s brushed and cleansed daily. 

** 16. They shall not allow the workers to leave any 
clothes in the dining-room, or their ordinary clothes in any 
work-room. 

** 17. They shall see that the supply of hot and cold water, 
soap, brushes, and towels is sufficient in the bath-room and 
lavatories. 

** 18. They shall see that there are kept in close proximity 
to the workers in each department washing conveniences and 
a sufficient supply of approved sanitary drink, and they shall 
cause the people to take it. 

**19. They shall set apart, and cause to be entered in a 
notice affixed in each department, a period of at least ten 
minutes, in addition to the regular meal-times, for washing 
immediately before each meal-time, and also before the end 
of the day's work ; and they shall see that it is observed. 

" 20. They shall see that at the doctor's weekly visit the 
proper entries are on each occasion made in the register. 

*' 21. Upon any person complaining of being unwell, they 
shall with the least possible delay give an order upon the 
doctor ; and upon any person desiring medicine, they shall 
give a dose of the prescribed medicine kept at the works. 

** 22. Managers, etc., shall report immediately to the firm 
any instance which comes under their notice of any worker 
neglecting the regulations hereinafter mentioned. 

** 23. They shall examine all persons going out of the 
works, and shall not allow them to leave unless they are 
properly cleansed from lead. 

'* Duties of Pebsons Employed. 

** 24. Each man or woman before commencing work in 
any of the following departments shall wear as follows, 
having received the same from the person in charge : — 



INOBGANIC PIGMENTS. 85 

** Blue beds — Every woman to wear an overall suit 
in all blue beds where the returns are used without 
being remelted. 
" White beds — One overall suit and head covering. 
Women inside the white beds to wear respirators 
also, but the * Carriers ' not. 
** Washing and crushing — One overall suit and head 
covering. ' EoUer ' women to wear respirators 
also. 
** Grinding — One overall suit and head covering, 
** Setting stoves — One overall suit and head covering. 
"Drawing stoves — One overall suit, head covering, 

and respirator. 
** Paint-mixing — One overall suit and respirator. 
" 25. Each man or woman working at any white bed, or 
in setting or drawing stoves, or in the washing and crushing, 
grinding, or paint-mixing departments, before going to break- 
fast, dinner, or home, or before entering the dining-room for 
any purpose whatever, must — 

** Put off the overall suit, etc., and give the same to 
the person in charge, or leave it in the clothes 
room. 
** Brush every particle of lead dust from his or her 

clothes. 
** Thoroughly wash face and hands in the lavatory, and 
be particular that no dust remain underneath the 
finger-nails. 
** If not wearing stockings and boots, thoroughly wash 
the feet. 
**26. Each man or woman must bathe at least once a 
week, and must wash in the lavatory before bathing. 

** 27. Each man or woman must receive and drink, at 
such times as may be stated in a notice affixed in the factory, 
such sanitary drinks as may be prescribed in such notice. 



86 CHEMISTBY OF PIGMENTS. 

** 28. Every white bed must be adequately watered on 
removal of the boards, and all trays of corrosions shall be 
well saturated with water before passing through the rollers. 
*' 29. No person shall smoke or use tobacco in any work- 
place, or room, or take food in any part of the works, except 
in the dining-room. 

** 30. No person may seek employment under an assumed 
name, or under any false pretence. 

** Eespirators — A good respirator is a cambric bag 
with or without a thin flexible wire made to fit 
over the nose. 

/'Sulphate of magnesia, 2 oz. 

** Sanitary drink suggestedi^ ' ?, ^ . 

Essence of lemon, sufficient 



to flavour. 



** Prescribed medicine. 



** The following Departments to he specially Ventilated. 

** (1) Washing and crushing. 
** (2) Grinding in water. 
** (3) Paint (grinding in oil). 
*' (4) Drawing stoves. 

**E. E. Speague Oram, 
** H.M. Chief Inspector of Factories. 

'' Under Section 9, Factory Act, 1891, any person who is 
bound to observe any special rules, as well as the occupier, is 
liable to penalties for non-compliance with such special rules." 

The composition of white lead varies somewhat, according 
to the method of preparation, as has been very frequently stated 
by different authorities. It may be represented by the general 
formula, xPbCOg yPb(0H)2, a hydrated basic carbonate of lead. 
Some samples approximate in composition to the normal 
carbonate ; others contain a rather excessive amount of 
hydroxide. The general opinion as to the normal composi- 



INORGANIC PIGMENTS. 87 

tion of this substance is that it contains two molecules of 
carbonate to one of hydroxide, 2PbC03Pb(OH)2. The excess 
of carbonate is usually supposed to be caused by the presence 
of free acetic acid towards the end of the process, as it would 
appear that it is only under such conditions that the normal 
carbonate forms, the product otherwise always being basic. 
A certain amount of normal acetate of lead is always present 
in unwashed white lead. One object of the washing is to 
remove this, but the amount is usually less in lead prepared 
by the English or Dutch processes than in that obtained by 
other methods, and it is in these two processes that the 
vinegar or pyroHgneous acid is allowed to evaporate quite to 
dryness, and fermentation of the dung or tan to go on for 
a further period, during which COg is evolved and most of 
the normal acetate converted into basic acetate, and then 
to basic carbonate. 

We give in the following table the composition of several 
samples of genuine white lead ground in oil, the composition 
of the oil-free white being given in the lower part of the 
table, and also the approximate molecular proportions of 
carbonate and hydroxide : — 

WHITE LEAD GROUND IN OIL. 





I. 


II. 


in. 


IV. 


V. 


VI. 


Oil, moisture, etc. 


6-5 


6-6 


7-2 


10-3 


7-3 


6-5 


Lead carbonate . 


71*3 


64-0 


66-3 


66-6 


67-0 


65-4 


Lead hydroxide . 


22*2 


29-1 


26-2 


23-2 


26-7 


28-7 


other matters 




•4 


1-3 






0-4 




100-0 


1000 


100-0 


100-0 


100-0 


100-0 




DRY MATTER. 










I. 


n. 


in. 


IV. 


V. 


VI. 


Lead carbonate . 


76-4 


68-6 


71-5 


74-2 


72-3 


69-2 


Lead hydroxide . 


23-6 


311 


.27-2 


26-8 


27-7 


30-4 


other matters 




•4 


1-3 






0-4 



100-0 100-0 100-0 1000 100-0 1000 
Molecular ratio — 

Pb(0H)2 : PbCOg 1 : 2-94 1 : 1-99 1 : 2-37 '1 : 2-69 1 : 2-35 1 : 2-06 



88 CHEMISTRY OF PIGMENTS. 

The foregoing figures may be taken as representing the 
composition of average samples of white lead prepared by 
dry corrosion. It will be seen that the molecular ratio, 
PbC03:Pb(OH)2, varies from almost 3:1 to 2:1. Samples 
have been examined by various authorities in which the 
ratio was as high as 5:1, but these are evidently quite 
abnormal. 

A sample of ** flake white " sold for decorators' use in 
large tubes had the following decidedly abnormal composi- 
tion : — 

Oil-Free Matter. 

Lead carbonate 94*1 

Lead hydroxide 3 "3 

Calcium carbonate, etc 2*2 

Fatty acids from lead soap . . . 0*4 

100*0 

It was ground with 9 per cent, of oil. 

We have examined samples in which the ratio, 

PbC03:Pb(OH)2, 

was very much lower than 2:1, but it is probable that none 
of these were stack-corroded. Some, we know, were pre- 
pared by other patent processes. We give the composition 
of some such samples : — 

Oil, moisture, etc. . . . 7*40 6*34 7*04 

Lead carbonate . . . 60*11 49*96 57*02 

Lead hydroxide . . . 42*49 43*70 35*94 

10000 10000 10000 

The following is a type of the enormous number of adul- 
terated samples that are frequently met with : — 

Oil 11*23 

Sulphate of lead 53*84 

Sulphates of lime and baryta . . 28*83 

Zinc oxide 6*10 

100*00 



INOBGANIC PIGMENTS. 89 

A pigment of astounding composition, sold as granitic 
flat white and ground in oil, contained — 

Oil / 7-9 

White lead 42-7 

Zinc sulphide 9*5 

Barium sulphate 39*9 

1000 

This on treatment with dilute acid evolved sulphuretted 
Tiydrogen with blackening of the pigment. It is a most un- 
suitable mixture for a white pigment. 

Undoubtedly much of the excellence of white lead as a 
pigment is due to its peculiar composition ; lead carbonate is 
a very fine opaque white of remarkable covering power, but 
alone it is neither chemically nor physically permanent as 
^n oil colour, as is shown by Prof. Church's experiments 
quoted in chapter ii. (p. 48), and the experiments quoted 
by Mr. Laurie, and referred to in our introductory remarks 
on this pigment; lead hydroxide, though not possessed of 
great pigmentary value, confers on the substance the most 
useful property of really combining with the oil in which it 
is ground, and, on drjnng, forming a hard and tough varhishy 
coat of oxidised oil and lead soap.^ It is for these two reasons 
that a white lead, containing an excessive amount of car- 
bonate, though beautifully white, is not very durable in oil 
on the one hand, and one too rich in hydroxide is possessed 
•of but little covering power or opacity on the other. 

^ On grinding with oil some increase of temperature is usually noted ; it 
is generally supposed that this is indicative of some saponifying process being 
set up, and when one reflects that lead plaster is prepared by warming litharge 
-and olive oil, it is not surprising that a (probably) much more active substance, 
finely ground lead hydroxide, should act in this way. That some sort of 
■saponification goes on is certain ; ether will not extract the oil completely 
from white lead, but when the apparently oil-free powder is decomposed with 
acid some traces of oil are usually found. 

The preference by painters for old white lead is easily explained when 
we consider that more saponification may be supposed to have taken place 
in such samples than in the freshly ground material. 



90 CHEMISTRY OF PIGMENTS. * 

One reason, it would appear, of the superiority of stack 
corroded over precipitated white lead is that the former is- 
always amorphous, while the latter is usually crystalline ; 
this being the case, however finely the pigment is ground, it 
is more transparent than the amorphous variety, and probably 
more light is lost by internal reflection, so that the brilliance, 
which is always desirable in a white pigment, is somewhat, 
reduced. 

The high price of white lead, consequent on the use of a 
somewhat costly raw material, and the lengthy nature of the 
process of manufacture, ofifers great incentive to adulteration 
and substitution. Various substitutes have been proposed 
and are sold as better than white lead, and a good deal is done 
in the way of dilution, or, as it is called, lowering with other- 
white pigments, of which barium sulphate is one of the most 
used (and cheapest). This fact renders the examination of 
this material a matter of some importance, and we therefore 
give a brief scheme for its analysis. 

The objects of an analysis of white lead being twofold,, 
(a) to determine the presence and, if present, the nature of im- 
purities ; and (b) to ascertain the proportion of hydroxide and 
carbonate. The following scheme will be fouqd siiflicient : — 

Determination of Oil. — A portion of 4 to 7 grams of the pig- 
ment ground in oil is weighed into a glass tube of about 30- 
cc. capacity and 20 cc. of ether added. The tube is corked,, 
and agitated until the white is uniformly diffused in the liquid^ 
and then it is placed in an upright position for some hours 
until the pigment has settled to the bottom, and then 5 cc. is 
pipetted off into a weighed beaker without disturbing the 
deposit, and the oil weighed after all the ether is evaporated. 
This method is suflSciently accurate for this purpose, though 
no correction is made for the volume of the oil present in 
the paint. How small this would be is shown by the follow- 
ing example : — 



INORGANIC PIGMENTS. 91 

Suppose 4 grams of a sample containing 8 per cent, of 
oil were treated with 20 cc. of ether and 5 cc. pipetted oflf and 
considered as J. Eight per cent, of 4 grams is '32 grams or 
•34 cc. of oil. If this dissolved in ether suffers no contrac- 
tion of volume, the whole volume of liquid will be 20*34 cc, 
and 5 cc. will be '246 of the whole instead of "250, and the 
weight of oil obtained will be '079 gram, equal to a result 
of 7'9 per cent, instead of 80 per cent., well within other 
errors of experiment ! The rest of the ether should be poured 
off this extracted portion of white, and one or two washings 
added to free from mechanically adhering oil, and the lead 
and carbonic anhydride determined in this. 

Determination of Lead, etc, — (1) About 1 gram of the pig- 
ment, either oil-free or ground in oil, is weighed into a 
beaker and treated with dilute nitric acid, the solution of the 
lead being hastened by warming either over a small flame or 
in the water bath. It is necessary that the beaker should be 
covered, as otherwise loss may occur by effervescence. When 
all action is judged to be over the liquid is filtered from oil and 
any other insoluble matter. The filter is washed with hot 
water and ignited with any insoluble matter (unless there is a 
great deal, when it should be burnt apart, and the insoluble 
matter added to the ashes) in a porcelain crucible. Occasion- 
ally a trace of lead is retained by the oil, and appears as in- 
soluble matter, in which case its amount should be added to the 
total lead. If more than 1 per cent, of insoluble matter is 
found its nature should be determined. Lead sulphate would 
be sufficiently soluble in strong hydrochloric acid to give a pre- 
cipitate of barium sulphate with barium chloride and of lead 
sulphide with sulphuretted hydrogen in very dilute solution. 
Barium sulphate would be entirely insoluble in HCl, but on 
fusion with alkahne carbonates (fusion mixture) would yield 
barium carbonate and alkaline sulphates, and either the Ba or 
the SO3 determined as BaSO^ would give the actual weight of 



92 CHEMISTRY OF PIGMENTS. 

barytes present. The filtrate and washings will contain 
all the lead (except part of any existing as sulphate) and 
other metals present. It should be diluted somewhat, 
nearly neutralised with sodium carbonate, and sodium 
acetate added, so that any acidity is due only to acetic 
acid. An excess of neutral potassium chromate is added to 
the warm solution, which is allowed to stand until the 
yellow precipitate of lead chromate has subsided, when the 
supernatant liquid should be poured off through a weighed 
filter and the precipitate washed once or twice by decantation 
with hot water, brought on to the filter and washed there, and 
when free from all salts, as shown by evaporating a few 
drops of the filtrate on a. glass slip, precipitate and filter 
may be dried in the water oven until of constant weight. 
The precipitate can, if preferred, be detached from the paper 
as completely as possible, the latter burnt carefully and the 
ash moistened with nitric acid and gently incinerated, and 
then the whole precipitate added to the (porcelain) crucible 
and gently ignited. The weight of lead chromate obtained 
X 0-689 = PbO or x 0-639 = Pb. The filtrate from the 
lead should be tested with ammonium oxalate for lime, which 
if present can be estimated by collecting the precipitate 
of calcium oxalate and weighing as CaCOg or CaO. The 
following mode of procedure (2) is perhaps more satisfactory 
in the case of adulterated samples. About 1 gram of the 
sample is treated with diluted hydrochloric acid on the water- 
bath in a moderate-sized beaker, and the liquid, when all 
action has ceased, diluted with boiling water and either kept 
on the water-bath or boiled over a flame. The hot liquid is 
filtered, the filter paper washed, any insoluble matter examined 
as above, and the filtrate largely diluted and cooled. To 
the cooled liquid sulphuretted hydrogen solution is added, 
or (better) the gas is passed through it until it smells 
strongly. The precipitate is collected on a filter and washed 



INORGANIC PIGMENTS. 93 

with water with a little HgS dissolved in it, dried, transferred 
as completely as possible to a crucible and either treated with 
HCl to convert into PbClg, or with H2SO4 to convert into 
PbSO^. The former should be dried at 200° C, the latter may 
be gently ignited until all free SO3 is evolved. Lead sulphide 
precipitated in HCl solution is never free from PbCla, con- 
sequently it is best to convert to PbClg or PbS04. 

PbCLj X 0-802 = PbO. 
PbS04 X 0-735 = PbO. 

The filtrate from the PbS should be examined for lime, 
which if present should be determined. 

Precipitation as sulphate of lead in the possible presence 
of lime is inadmissible ; if, however, SO3 is found to be present 
in the sample it is best to treat a weighed portion with 
HCl or HNO3, dilute, filter if necessary, and determine the 
SO3 either (with the addition of alcohol) as PbSO^ or (much 
better) by addition of barium chloride and precipitation as 
BaS04. The weight of SO3 found should be added to any 
found in the insoluble portion as PbS04, and according as 
PbS04, or lime, is present, calculated as lead sulphate or 
calcium sulphate. 

Determination of Carbonic Anhydride. — A portion of 4 to 6 
grams of the oil-free pigment is either decomposed in a small 
flask and the CO2, after being freed from HCl by copper sul- 
phate (on pumice) and dried by sulphuric acid, is absorbed 
by caustic potash or soda lime, the increase in weight of 
potash balls or soda-lime tubes being equal to the amount of 
CO2 present, or (less satisfactorily) a loss apparatus of the 
Schrotter type is used. The percentage of COg is calculated 
back to the original white in oil, 

CO2 X 6-066 = PbCOj. 

All the CO2 found, except in cases where lime is present 
and SO3 absent, is calculated as PbCOg, but should lime be 



94 CHEMISTEY OF PIGMENTS. 

present and no SO3, all the COg not required to form CaCOg 
is calculated as PbCOg, and the excess of lead oxide over the 
amount required for the CO2 calculated to Pb (0H)2 ; PbO x 
1-08 = Pb (0H)2. The ratio PbCOg : Pb (0H)2 is thus obtained. 
Lead sulphate, lime compounds, barytes or china clay can only 
be regarded as adulterants ; the only object of adding them is 
to reduce the cost, and their presence and amount should be 
stated with, we think, a decidedly adverse comment should 
calcium sulphate be present, as this is more or less hable to 
be acted on by water. The others are quite inert, and 
though they decrease the covering power of the pigment, in 
some cases the lower price of the article may be considered 
as a set-off against this ; any amount of such diluents is, in 
our opinion, objectionable, as by their presence the peculiarly 
good qualities of white lead are reduced. 

White lead is usually used in oil, both as a white paint 
and as priming or preliminary coats to a new surface which 
is finally to be coloured. The colouring matter or ** stain" is 
seldom applied alone, but is diluted with white, in most cases 
preferably white lead, to the required tint. By this means 
colours of poor covering power or bad drying properties will 
form an opaque, quick drying, tough and impervious coat. 
It is as an oil colour that the peculiar excellencies of white lead, 
both as a protective coating to wood or iron and as a covering 
substance from the colour point of view, are most apparent. 
White lead will, however, work well in water, and was 
formerly used considerably when a white pigment was re- 
quired for water colour. It is not, however, nearly so suitable 
for this purpose as other white pigments which will be dealt 
with in this chapter. White lead is known to the artist in 
oils as flake white and is one of his most important pigments, 
being used both as a priming for his ground, for diluting other 
colours and for putting in high lights, either white or white 
glazed over with other transparent colours. It works well 



INORGANIC PIGMENTS. 95 

^th most other colours, but is inapplicable in conjunction 
with coloured sulphides which are liable to cause blackening 
by formation of lead sulphide. The yellowing by age of flake 
white in oil paintings has been before alluded to ; it seems to 
be rather a change of the lead-oil varnish than any ordinary 
•deterioration, and is not often so pronounced as to be un- 
pleasant. 

Zinc White. 

This extremely brilliant white pigment was introduced 
some years ago in the hope that it might replace white lead. 
This it has altogether failed to do ; it is nevertheless a very 
fine pigment and possesses very fair covering power, not, 
however, equal to that of white lead. Its colour is rather 
s. bluish white. It works well in oil and extremely so in 
water, and is the water-colour white par excellence. 

Zinc white is the only definitely known oxide of zinc ; its 
composition, expressed by the formula ZnO, corresponds to the 
known salts of zinc. It is prepared by distilling zinc in clay 
retorts connected with a series of chambers through which 
air is blown. The zinc volatilises and combines with oxygen 
in so doing, and the clouds of zinc oxide formed collect on 
the walls of the receiving chambers as an amorphous deposit 
easily reducible to powder. This is levigated to separate from 
any unaltered zinc, and the settled and finely ground oxide 
collected and dried. It is then ready for mixing with either 
oil or water. Zinc white can also be prepared by oxidising 
zinc in large muffles. 

As it is a very high-priced material, zinc oxide is subject 
to considerable adulteration with other less expensive whites. 
The following scheme will suffice to detect and determine any 
ordinary adulteration : — 

Determination of Oil, — As suggested for white lead (p. 90). 




96 CHEMISTRY OF PIGMENTS. 

A correction should be made for the volume of oil in solution* 
in the manner suggested. 

Determination of Zinc and of Impurities, — A portion of 1 to- 
2 grams is digested with dilute hydrochloric acid on the 
water bath or over a flame until all is dissolved (except 
oil) or until no further solution takes place. The liquid is- 
then filtered and the filter paper with any insoluble matter 
ignited and the nature of this insoluble portion determined as 
described under white lead (p. 91). The filtrate is diluted 
to a known bulk and the zinc determined in a portion cor- 
responding to from "5 to 1*0 gram of the original, either (1) by 
titration with potassium ferrocyanide or (2) by precipitation 
as sulphide. 

(1) Titration with ferrocyanide. A solution of potas- 
sium ferrocyanide containing 41*25 grams of the salt per litre 
is standardised by means of pure zinc. About "5 gram of 
zinc foil is carefully weighed and dissolved in dilute HCL 
The solution is raised to boiling, two or three drops of a 
solution of uranium nitrate or acetate added and the ferro- 
cyanide solution run in from a burette until the brown colour 
which at first forms and disappears almost at once becomes 
more persistent. When this is the case portions are taken 
out of the vessel on the end of the rod used for stirring and 
tested with uranium on a tile until a reddish brown colour 
is produced. This indicates excess of ferrocyanide ; the 
volume used should be noted, "1 cc. deducted for the amount 
required to produce the colour and the value of 1 cc. in zinc 
calculated; this should be "01 gram almost exactly. The 
titration of the solution containing zinc should be made in 
exactly the same way as that wdth pure zinc. The method 
is expeditious and accurate, copper and iron being the only 
interfering substances. Neither is likely to be present in 
zinc white, but copper gives a chocolate and iron a blue 
precipitate with ferrocyanide, so their presence would soon be 



INOEGANIC PIGMENTS. 97 

noted. When the zinc ferrocyanide has settled and left a 
clear supernatant liquid this can be decanted and tested 
for lime. The addition of sulphuretted hydrogen to another 
portion of the original liquid will indicate the presence or 
absence of lead. Any other white than white lead or calcium 
carbonate would be found in the insoluble portion. 

The zinc found is of course calculated as ZnO. The 
percentages of zinc oxide, oil and insoluble matter should 
add up to 100 approximately, if no calcium carbonate or white 
lead be present. Should either lime or lead be found and it 
is desired to determine their amount by a direct method — 

(2) A definite portion of the HCl solution is treated with 
sulphuretted hydrogen, being previously considerably diluted 
if it is not already fairly dilute. Any precipitate in this acid 
solution is probably lead sulphide. This should be collected 
on a filter, washed with H^S water (diluted), dried and 
weighed as sulphate. This can be examined qualitatively 
if desired. The filtrate is made alkaline with ammonia, 
allowed to stand for some time, and the resulting precipitate 
of zinc sulphide collected on a filter, washed, redissolved in 
dilute HCl and zinc carbonate precipitated by Na.^C03. This 
is collected, washed, dried and ignited (the filter being ignited 
separately and the ash added), and weighed as ZnO. Or the 
dissolved zinc sulphide may be titrated with ferrocyanide as 
above (1). 

We give the results of examination of some samples of 
this pigment which have come under our notice. 

Oil ... . l'-93 17-72 19-17 20-6 
Zinc oxide . . . 82-07 82-28 80*83 79-4 



100-00 100-00 100-00 10000 



The above samples as will be seen were all pure. The 
amount of oil necessary for grinding to a pasty consistency 
varies a few per cent, either side of 20 (of the whole, or 25 




98 CHEMISTEY OF PIGMENTS. 

per cent, of the weight of white). The following is the com- 
position of an adulterated sample we have recently met with. 

Oil 140 

Zinc oxide 56-8 

Zinc sulphide 210 

Barium sulphate 82 

100-0 

Zinc sulphide is sometimes used as zinc white and its 
use seems quite legitimate, but this sample is also diluted 
with barium sulphate. It looks like an order made up when 
the stock of oxide had run short. The reduced proportion 
of oil is very marked, though the sample was quite as pasty 
as is usually the case. The sample was of a very bluish 
white. 

The following is typical of many samples we have met 
with : — 

Zinc oxide 56*0 

Barium sulphate 34-5 

Chalk 9-5 

One advantage of zinc oxide is its absolute permanency 
in sulphur-laden atmospheres. Mr. H. Smith's experiments 
quoted previously show that as a protective colour zinc white 
takes a very high rank, and this notwithstanding the general 
opinion that it is absolutely inert to linseed oil. It would 
certainly at first sight appear that the oxide of so strongly 
electro-positive a metal as zinc should have some saponifying 
action on oil and not be, as is supposed, merely suspended in 
the hardened oxidised oil coating. 

Zinc white in water colour is usually known as Chinese 
white. 



INORGANIC PIGMENTS. 99 

Enamel white {Blanc Fixe, Permanent White, Barytes White, 

Barium Sulphate). 

Barium sulphate occurs in nature as barytes, barite, heavy 
spar, or schwerspath, in crystals of the orthorhombic series. 

It should be fairly pure, and require no further preparation 
than grinding to a fine powder and treating with hydrochloric 
acid to remove any soluble matters. 

Barytes is used to some slight extent as an oil white, 
but is too crystalline, and, therefore, transparent, to be of 
much use. Its principal use, or abuse, is to dilute white 
lead and other expensive colours. Its specific gravity, 4*3 
to 4*72, is in its favour for such purposes. 

It should be entirely insoluble in hydrochloric acid ; any 
effervescence would indicate the presence of carbonate. The 
insoluble matter, on fusion with mixed carbonates of potash 
and soda, should, on extracting with water and treating 
the aqueous solution with hydrochloric acid until acid, and 
then precipitating with barium chloride, yield its own weight 
of barium sulphate, or the insoluble portion dissolved in 
hydrochloric acid and precipitated with sulphuric acid should 
also yield its own weight of barium sulphate. 

On fusion 

Ba SO4 + M'2 CO3 = Ba GO3 + M2 SO4 ; 

therefore the weights of barium sulphate obtained by either 
precipitating the Ba or the SO4 should be equal. 

Whitening, Chalk {Calcium Carbonate). 

Prepared chalk or whitening obtained from native chalk 
by a process of washing over is used to some extent as a 
diluent in oil colours, and also for tempera (** distemper **) 
and whitewash. It is, as sold, tolerably pure calcium car- 
bonate, CaCOg. It should be entirely soluble in dilute hydro- 
chloric acid (absence of sand, clay, etc.) to a colourless 



100 CHEMISTRY OF PIGMENTS. 

solution, give no precipitate when ammonia is added in slight 
excess to this solution in the presence of ammonium chloride 
(enough of this is usually formed in neutralising the excess 
of hydrochloric acid), indicating the absence of iron and 
alumina. More than traces of iron would spoil the pure 
white of calcium carbonate. It should, on determination of 
CaO and COg, agree closely with the composition : — 

CaO 66 

GOa 44 



1000 



II.— OXIDES OF LEAD. 

Red Lead {Synonym — Minium PbgO^). 

This very brilliant scarlet, or rather perhaps scarlet-pink 
lead pigment is not now very much used alone, but prin- 
cipally mixed with white lead as a priming coat. It is 
possessed of remarkable drying properties in oil, and forms 
a splendid varnishy compound with it. It is usually used 
with raw linseed oil, as it dries too quickly and with a too 
brittle surface if used with boiled oil. 

Eed lead is prepared by heating massicot or litharge 
(PbO) in furnaces to a temperature not exceeding 800° C. 
Under these conditions it absorbs oxygen from the air, and is 
converted into the red powder known as red lead. It is 
usually supposed to have the composition Pb304 = 2PbO 
PbOg, but Mulder has found samples of the composition 
Pb^Os = 3PbO PbO^. 

We have examined many samples of this pigment, and 
have found the percentage of lead to correspond tolerably 
well with PbgO^, though the difference in percentage composi- 
tion of the two oxides is not great, as the following figures 
show : — 



INORGANIC PIGMENTS. 101 

Lead 90-66 9118 

Oxygen .... 9*34 8*82 



lOO-OO 10000 

The following percentages of lead were obtained by us in 
some of the samples examined : — 

89-90. 90-28, 89*60, 9138, 91*09, 8994. 

Amounts of insoluble matter never greater than 1 per cent, 
have been found by us ; this insoluble matter appeared to be 
sand or clay, and was without doubt accidental. 

Eed lead has a specific gravity of 8*62 — 9*19, is 
crystalline in structure, darkens on heating, but recovers its 
colour, and on heating very strongly gives oJ9f oxygen. It is 
not entirely dissolved, but is darkened, by nitric acid, which 
dissolves out the monoxide as lead nitrate, and leaves the 
dioxide PbOg as a purple-brown powder. 

Red lead will dissolve easily iii nitric acid if a little sugar 
or starch is added. This is oxidised partly at the expense of 
the lead dioxide, and if the acid is somewhat dilute the lead 
passes into solution as plumbic nitrate ; if the acid is concen- 
trated the nitrate separates in crystals, but can be dissolved 
by dilution with water. The lead can be determined in this 
solution, after filtration from any insoluble matter, which 
should be weighed, by either of the methods recommended in 
the section on white lead. Red lead also dissolves in hydro- 
chloric acid with evolution of chlorine. If it is decided to 
determine the lead either as chloride or sulphide, hydrochloric 
acid is a suitable solvent. The action of hydrochloric acid 
on red lead affords a means of determining the proportion of 
dioxide. When lead dioxide or red lead is treated with 
hydrochloric acid, 

PbOg + 4HG1 = PbCLj + Cl^ + 2H2O, 

or 

Pb304 + 8HC1 = 3PbCl2 + Clg + 2H2O. 



102 CHEMISTRY OF PIGMENTS. • 

If the chlorine thus liberated be passed into a solution of 
potassium iodide, using a suitable form of distilling and ab- 
sorbing apparatus to ensure complete absorption, then an 
equivalent amount of iodine is liberated, 

2K1 + CI2 = 2KG1 + Ig. 

This iodine may be titrated with standardized thiosulphate 
and so, indirectly, the amount of peroxide contained in the 
red lead determined. For technical purposes it is usually 
sufficient to ascertain that it is a pure oxide of lead of the 
right shade. 

Litharge {Massicot, Lead Monoxide^ PhO). 

In addition to the hydrated carbonate and the red oxide 
of lead, the monoxide, litharge or massicot, is used to some 
extent. This is prepared by heating lead to above its 
melting point in the open air. It forms a reddish-yellow 
scaly mass, or an amorphous powder, according to whether 
the temperature has been sufficiently high to cause fusion. 
It possesses marked basic properties, and easily enters into 
combination with oils to form lead soaps. For this reason 
it is used with linseed oil as a *' drying " material. It dries 
too well to be suitable for use as a pigment, as the coat 
formed is too hard to wear well. Its principal use is as a 
drying material for paints and oil varnishes. 

Some other lead pigments but little used now are : — 

Bed'hrown, ioTTDLQdi by the fusion in a clay crucible of 1 
part red oxide of iron with 10 parts of red lead. 

Orange mineral, a variety of red lead formed by the 
calcination of white lead. Mulder gives its composition 
as : — 

Lead monoxide (PbO) 73 

Lead dioxide (PbOg) 25 

Carbonic anhydride (COg) 2 

too 



INOBGANIC PIGMENTS. 108 

Mr. A. p. Laurie in his Cantor Lectures says of red lead : 
'* It was prepared by roasting white lead. It is now, I 
believe, usually prepared from litharge. No doubt the 
minium prepared from white lead would be a finer pig- 
ment.*' 

III.— MERCURY PIGMENTS. 
Vermilion-. 

This very fine scarlet pigment is a sulphide of mercury 
corresponding in composition with the mineral cinnabar — 
mercuric sulphide HgS, in fact ; occasionally specimens of 
cinnabar are found sufficiently bright for use as a pigment, 
more often, however, vermilion is prepared artificially from 
mercury and sulphur. 

There are two classes of processes by which this pigment is 
prepared — dry processes in which the combination is effected 
by means of dry heat, and the product prepared by sublima- 
tion, and wet processes in which both the combination and 
further preparation are effected by the aid of liquids. 

The procedure in both processes is first to prepare the 
substance known as Ethiops mineral, a blackish sulphide of 
mercury with uncombined sulphur, and then by suitable 
treatment to produce some molecular change by which the 
substance becomes of a bright scarlet colour. 

We give some examples of each class of processes : — 

Dry Processes. 

At the mines in Idria the following process is adopted — 
85 parts of mercury and 15 parts of sulphur are ground 
together in revolving tuns for some hours until combination 
appears to be complete. The ** Ethiops *' thus formed is 
then heated in cast-iron cylinders and sublimed thence into 
clay condensers. 



104 CHEMISTEY OF PIGMENTS. 

The process used in Holland is said to consist in preparing 
the *'Ethiops" with 1 part sulphur, 2 parts mercury + 2*5 
per cent, finely divided lead or red lead. Lots of about 
100 kilos are sublimed and the sublimate allowed to cool 
slowly during twenty hours, and then finely ground and 
levigated. 

Another process is to gently heat 75 kilos sulphur, and 
540 kilos mercury on a shallow iron pan, and break up the 
'* Ethiops,*' which is kept in jars until it is wished to sublime 
it. The contents of two or three jars are emptied into a tall 
clay pot, the bottom of which is heated in a furnace to a dull 
red. The substance inflames as it is thrown in owing to 
the combustion of the excess of sulphur, and as the flame 
goes down a stout well-fitting iron cover is placed on the 
pot. A fresh charge is added every four to five hours, and the 
heating continued for thirty-six hours. After cooling the pot 
is broken, and the vermilion scraped from the lid and top 
of the pot. The sublimate is then finely ground and levi- 
gated. 

The shade is sometimes modified by treating with hot 
alkaline solutions which, perhaps by removing traces of un- 
combined sulphur, possibly by favouring some molecular 
change, brighten and purify the colour. 

The object of sublimation appears to be twofold, firstly, to 
remove excess of sulphur, which as being the cheaper material 
is always used in considerable excess, as the percentage com- 
position of mercuric sulphide shows ; — 

Mercury . . . 86-2 ) 

Sulphur . . . 13-8 ,- S : Hg = 1 : 6-2 



1000 



and, secondly, to cause the change which results in the 
formation of a scarlet sulphide. 



INOEGANIC PIGMENTS. 105 

Wet Processes. 

In China vermilion of a high quahty has been prepared 
probably for many centuries. The process used is sup- 
posed to be a wet one.^ 

We give some examples of European wet processes : — 

Kirchoffs Process. — Three hundred parts mercury and 68 

parts sulphur are moistened with a little potassium hydroxide 

(caustic potash), and ground together for some time. The 

black ''Ethiops" which forms is then mixed with 160 parts 

^ The following process, which is certainly not a wet one, is given in 
Thorpe's Dictionary of Applied Cliemistry as that by which Chinese vermilion 
*' is said to be prepared ". 

" About half a bottle (38 lb.) of mercury and 17J lb. of sulphur are 
mixed in an iron pan about twenty-five inches wide and seven or eight inches 
cleep, heated by charcoal. When melted it is stirred with an iron spatula, 
and the remainder of the bottle of mercury is gradually added. When the 
metal has disappeared it is removed f lom the fire, cooled by the addition of 
a little water, rapidly stirred and coarsely powdered. The reddish or black 
semicrystalline powder, which contains free mercury and sulphur, is placed 
in a fixed iron pan, and covered with porcelain tiles eight inches in diameter 
{many of which are broken), arranged in the shape of a dome. The whole 
is covered by a pan four inches in diameter less than the fixed one, to which 
it is luted by clay, leaving four holes in the luting for the escape of gases. 
The charcoal fire is then lighted and kept fiercely burning for eighteen hours ; 
blue flames are seen burning round the holes, showing loss of sulphur and 
of mercury. The fires are then allowed to die out, and the pans to cool. 
Most of the vermilion is found adherent to the porcelain and is removed. 
That attached to the iron is inferior, and is made with the other waste 
into cakes with alum and glue-water, dried and resublimed. The sulphide 
on the porcelain is blood red and crystalline. It is powdered and ground 
with water in a hand-mill between stones, and washed in a vessel. At the 
close of a day's work, a solution of alum and glue (1 ounce of each to 1 
gallon of solution) is stirred well with the powder, and the whole is allowed 
to stand until morning. The glue tends to lengthen the period of deposition, 
and to render the stratification into the various qualities more perfect. The 
alum is said to improve the colour. The liquid is decanted, and the upper 
portions of the deposit are set aside. The lower parts are reground and 
treated as before, the grinding being sometimes repeated several times. The 
fine vermilion is stirred in water and settled, and the water is decanted. 
The residue is dried in the open air, powdered, sifted through muslin and 
packed in papers holding about I^ ounce each." 



106 CHEMISTRY OF PIGMENTS. 

of potassiuiD hydroxide dissolved in a very little water and 
heated to boihng for thirty minutes. Water is added to keep 
up the volume of the pasty mass, which is stirred well, and 
first becomes brown and gelatinous and then red. This 
mass is stirred until cold, and then washed free of alkali, 
ground and levigated. 

Briinner's Process. — Three hundred grams mercury, 114 
grams sulphur and 75 grams potassium hydroxide dissolved 
in 450 cc. water are taken. The mercury and sulphur are 
ground together, and the alkali poured on the mixture in 
small portions until all is added. The mass is well stirred, 
and then heated for seven to eight hours at a temperature 
of 45° to 50° C, £he volume being maintained by additions of 
water. The mixture, which is black to begin with, under 
the action of the alkali becomes brown, red, and finally scarlet. 
The vermilion is well washed from all alkaU, ground and 
levigated. 

Jacqiielin used a similar process, but the following propor- 
tions, 90 parts mercury, 30 parts sulphur, 20 parts potassium 
hydroxide, 30 parts water, and heated to 80° for one hour 
instead of seven to eight hours at 45° to 50°. 

Firmerich prepared a very fine vermilion by the action of 
(pent a) sulphide of potassium on mercury. 

Potassium sulphide is prepared by igniting potassium 
sulphate with charcoal, extracting with water and concen- 
trating to remove unaltered sulphate, which, by reason of 
its somewhat sparing solubility, crystallises out. The solu- 
tion of sulphide thus prepared is boiled with sulphur. By 
this means the polysulphide is formed. This method is 
found to be more satisfactory than fusion of potassium 
hydroxide or carbonate with sulphur, as in these methods 
other products than penta- or other poly-sulphides are formed. 
Five parts of mercury, 1 part of sulphur, and 2J parts of 
sulphide solution (on the basis of 2 parts K2S to 7 parts 



INORGANIC PIGMENTS. 107 

water) are placed in bottles, moderately heated to start action, 
and continually shaken for three and a half hours ; a greenish- 
brown product results. This is cooled and kept for two to 
three days in the '* stoveroom " at a temperature of 45"* to 50"* 
C. ; after cooling, the vermilion is carefully treated with sodium 
hydroxide to remove unaltered sulphur, and the alkali is 
then removed by washing with water. 

The object of the addition of sulphur to the mixture of 
polysulphide and mercury is to replenish the former sub- 
stance, which acts as a carrier of sulphur, and to effect a 
combination which would otherwise require the aid of a dry 
heat. In the other wet processes the solution of potassium 
hydroxide used, by causing the formation of sulphides and 
other sulphur compounds, enables the whole, or nearly the 
whole, of the mercury used to be converted into sulphide. 

Various means are used to improve and to fix the colour 
of vermilion prepared by either process. Treatment with 
nitric acid to remove any uncombined sulphur ; with a mix- 
ture of potassium sulphide and hydroxide with hydrochloric 
acid, which should remove any alkalies ; and with hot potas- 
sium hydroxide solution, which is said to give a violet tinge, 
are processes which have been recommended for these pur- 
poses. The main object seems to be to obtain a very pure 
red material corresponding, as far as is reasonably possible, 
to pure HgS. This, whatever tint may be obtained, is 
less likely to alter in tint than a substance which is not a 
chemical individual. 

The examination of vermilion is not usually a matter of 
great difficulty. It is generally sufficient to agitate a portion 
with alcohol, and allow to settle, filter off the alcohol, 
and notice the colour of the solution, and determine the 
amount of ash left on ignition at a moderately low tempera- 
ture. The former test indicates the presence or absence of 
eosin, which would give a pink colour and coppery fluores- 



108 CHEMISTRY OF PIGMENTS. 

cence to the alcohol, or of other dyes which might be used 
to brighten the pigment, while the presence or absence of 
any amount of ash is a criterion of the amount of inorganic 
adulteration. 

Eed lead and scarlet antimony sulphide are, we believe, 
used more or less as adulterants. These, unless present in 
considerable quantity, have no great effect on the colour of 
the pigment, though, are of course, undesirable. A mixture 
of barium sulphate, red lead, a little vermilion, and eosin to 
brighten the mixture, forms a not uncommon substitute for 
vermilion. If any residue over 1 or 2 per cent, is left in igni- 
tion it is well to examine its nature with a view to detecting 
adulteration or carelessness in manufacture. Small quan- 
tities of ferric oxide (under 1 per cent.) are frequently found in 
vermilion. This is, doubtless, derived from the vessels used 
in manufacture, and in such small quantities must be 
regarded as accidental and allowable, though a treatment 
with warm dilute hydrochloric acid should remove the greater 
part of this impurity. Alkali, or alkaline salts, other than 
mere traces, would indicate imperfect washing and probable 
formation by a wet process. 

Eosin is sometimes added to a pure vermilion, not, in 
this case, to cover the admixture of a white substance, but 
to brighten a badly prepared and probably over-heated 
pigment. In any case its fugitive nature renders its presence 
in colour intended for any but the most temporary purposes 
extremely undesirable. 

Chinese vermilion, which is greatly esteemed for its 
beautiful full colour, usually contains a small quantity of 
organic matter, apparently glue, but not in sufi&cient quantity 
to be in any way objectionable. 

Should it be considered in any way desirable to determine 
the mercury in this substance, a portion of, say, 10 grams 
should be mixed with pure quicklime and ** burnt " in a com- 



INOEGANIC PIGMENTS. 109 

bustion tube packed in the usual manner. The arrangement 

of the ingredients in the tube, starting from the front end, is 

as follows : — 

Lime and iron or copper. 

Vermilion and lime. 

CO2 mixture. 
The best plan is to weigh the vermilion on to 10 to 20 
grams of freshly ignited lime in a glass or porcelain 
mortar, and then fill in, either by a funnel or by scooping 
with the tube itself into a clean dry combustion tube of about 
f to J inch internal diameter, closed at one end, and with 
2 to 3 inches of a substance to evolve COg,^ already filled 
into the closed end, and plugged down with asbestos. 

,^.,...^ 1 

iiiiiiiilSiiiiiiiiii^^ 

> > 

m m 

o o 





Fig. 4. 

The mortar is then rinsed out with one washing of lime, 
and a plug of asbestos inserted in the tube, after which a further 
portion of lime is filled in. A layer of copper turnings, gauze 

^ The following substances are suitable to use for the evolution of CO2 : — 

1. A mixture of 3 parts fused potassium bichromate with 1 part of ignited 
anhydrous sodium carbonate, both finely powdered, and then intimately 
naixed. This is a very good and sensitive mixture. On ignition — 

KgCraOy + NaaCOg = K2Cr04 + Na2Cr04 + CO2. 

2. Sodium bicarbonate. On ignition — 

2NaHC03 = NaaCO, + H2O + COj. 

3. Magnesite. On ignition — 

MgC03 = MgO .+ CO2. 

4. Oxalic acid, anhydrous. On ignition — 

POOH ~ ^^2 "^ ^^ "^ OH2. 
1 and 3, which give dry CO2, are preferable. 



110 CHEMISTEY OF PIGMENTS. 

or spirals of wire, or of iron nails or wire, about 3 inches 
long, is then filled in, and the tube drawn out obliquely 
and (when cooled) placed in a combustion furnace, the drawn- 
out part dipping well below the surface of water in a flask 
or beaker. The heating is started from the open end of 
the tube, and when 3 to 4 inches of lime are red hot, 
one burner at a time should be lit, and also one burner 
at the back under the plug of asbestos by the COg mixture 
to prevent sublimation back, and to start a stream of COg, 
which should be maintained, so as to secure constant bubbling 
of gas through the water (thereby preventing a back rush 
of water). When the whole of the lime is red hot all 
the burners should be lit so as to sweep over all the mercury 
vapour. Then, when no more globules of mercury condense, 
the curved part of the tube is broken by touching it with a 
wet file or glass rod, and any mercury which may have 
accumulated in this front part is washed into the flask and 
gently agitated to cause the globules to cohere, the water 
poured off as completely as may be, and the mercury trans- 
ferred to a weighed porcelain capsule, the visible water being 
removed by blotting paper, and the mercury dried at a low 
temperature in a desiccator and weighed. 

The use of copper or iron is necessary in the case of 
mercuric sulphide, as otherwise sulphide may sublime over, 
or, if water vapour be present, sulphuretted hydrogen be 
formed. In either case the heated metal retains the sulphur 
and allows the mercury to pass over. 

The action of the lime may be represented as follows : — 

2HgS + 2CaO = 2CaS + 2Hg + O2. 

Some of the calcium sulphide is probably oxidised to sulphate 
by the oxygen liberated. 

The action of the iron or copper is : — 

M" + HgS = M'' S + Hg, 

or 

M" + H«S = M" S + H„. 



This tiry -ii^^nllibaitic. z^eii-ni i-s- "^"^^ **:•.: :irA3c iH'I-ftrti. C'^s 
in oniinary w r-rk -^ 'erjA. ~ I7 ^l»i« ni --rr^trSiiArT 

When. ^t^- ^--"-. r £r: :L:i«i iz. :l1 i> •exizm-Tti i prn:;:: 
should fee fretrii ±r:ci :•!, Aa> r-r«^:nii^'fi.i-ni in ii-r v.nk:?«e 0: 
iflrhite lead *zii ■iiLi'fr r.-zm-T-'T'. azli r^.siz. j.«:kTii ::r in 
the ethereal •=*:!":::•: ci, TTie iLl-fr^re niirier :> li^med. and. 
if necessarv. zhft rziiii~L-T -^ Tk- — >^* \^~:L-rr. a iriemunjiJr:;!: 
of the oil i^ n::! ■^:cL-?i-irr-fii "►fi-^s&trr. n ttiH ce >:i:r:c:t?-:i!r 40 
shake up wiih ezL^z ani f li^rr :r iii-r -?* -::r: r.. exar::^.:::^ ::> 
colour, and 10 i^niie a it rn - :: il-r :1t L:.ij.rr:AL 

The nature >:: trir-i/. .-r i.til:rrri:i:.> :f Trmiil::!: his Ween 
indicated in tL-e tr'^of^i:::^ titTA^Tirl-^- KiTin^ record to 
the hisrh specif::- zriTirr :: T-rri-iil: : !i. i: i> ctiozis ihiki very 
fe^r adulterani<3^ einl-i te ;i.^i«eii in any aniiunt wiihrat so 
seriously reiin-i-m^ ^e si^trijin:- iravirv :: the material thai it 
liirould be aprareni i*:- :he user. 

We have oo:-asi : nallv exaniin^i ai'ilrerated samples of 

■k. 

vennihon. ani als«> sanities •'.■f niercnrfo snip hide briirhtei^tHi 
\rith eosin : d .ifciless these laiter were badly prepared, and 
"faked" in this manner to av id the eo>t of resubliuiation. 
The coniposition ot two of these is ^ven t«el«>w : — 

Merc-nrir s-IpL.ic .... 5S-9 50 

BarizjE. i-zL^'cjiZe .... 1^-0 — 

Lead siilpiiare .... 291 49 

£osiii — 1 

lOCK) 100 

W^e also give the conipDsition of some genuine samples : — 

Moisture 0-4 0-5 — — 

L*08s cm ignition 'HgS> . 99-1 99-2 !^1 994 

Non-ToUtile matter 0-5 0-3 0*9 0^ 

100-0 lOOK) 100-0 100-0 

The non-volatile matter was either clav or oxide of in^n. 
imth traces of alkah in the case of the last sample (, = under 
003 per cent. KHO). 



112 CHEMISTRY OF PIGMENTS. 

Vermilion, notwithstanding its extreme brilliance and 
good body, has a rather bad reputation for permanence. It 
would appear to be somewhat liable to molecular change, 
as it is stated that exposure to daylight has changed from 
red to black vermilion letters in illuminated books exhibited 
in museums, which had remained intact for hundreds of 
years with the limited exposure incurred in use. It must 
at the same time be admitted that vermilion frequently will 
retain its colour for a long time and under trying circum- 
stances. Being a very inert substance and a sulphide, it is 
not easily changed in composition, or in any way chemically 
affected by any reasonably possible use except, of course, 
at very high temperatures, and, as we have before stated, 
the liability to molecular change appears to be much reduced 
by careful removal of impurities, and in the case of the dry- 
formed material by condensation at a high temperature. 

It must be remembered that vermilion is used for paint- 
ing out-door work by both Post Office and Fire Brigade 
authorities, and that it stands well on their carts and pillar- 
boxes under very trying conditions. We know that in the 
case of the Metropolitan Fire Brigade great care is exercised 
in the selection of vermilion for this work, and doubtless 
the Postal authorities exercise similar care. 

We think that in many modern cases of serious deteriora- 
tion of so-called vermilion, an examination of the colour 
would have shown it to be a *' vermilionette," the fancy 
name for adulterated, brightened scarlets, some of which 
are almost innocent of mercury. 

Royal Scarlet {Mercuric Iodide). 

This pigment is prepared by the double decomposition of 
solutions of mercuric chloride and potassium iodide. It is, 
as both these substances are expensive, desirable to use 
molecular proportions. The proportions 4 mercuric chloride 



INORGANIC PIGMENTS. 113 

to 5 potassium iodide agree very closely with those required 
by the scheme. 

HgCl^ + 2KI = Hgl, + 2K01. 
271 332 454 

Though a very brilliant colour, mercuric iodide is not to 
be recommended. 

IV THE CHROMIUM COLOURS. 

Two series of colours owe their tints to the presence of 
the element chromium, the chromium oxide greens and the 
yellow and red chromates. The former contain as the colour- 
ing group the oxide CrgOg, sometimes as hydroxide, some- 
times as phosphate, while the latter owe their colour to 
chromic anhydride CrOg. 

The Chromium Oxide Greens. 

Chromium oxide, CrgOg, prepared by ignition of the 
hydroxide, or by the methods given below, is a sage green 
coloured substance easily worked in water or oil, and abso- 
lutely permanent as to tint, being not only unaffected by 
light, but also unattacked by acids or alkalies. It is insoluble 
in concentrated acids, and can only be brought into solution 
by fusing with an oxidising mixture such as sodium carbonate 
and potassium nitrate, or chlorate, when it is converted into 
chromic anhydride, thus : — 

CrgOi + 30 = 2Cr03. 

This is found in the product of fusion as alkaline chromate. 

On account of its permanency chromium oxide is a 
colour much esteemed by artists. We give some methods 
of preparing it ; they are mostly based on the reduction of 
chromates and bichromates. 

(a) By the ignition of mercurous chromate (the brick- 
red precipitate obtained on adding a soluble chromate to a 

solution of a mercurous salt) a very pure and fine-coloured 

8 



I 



114 CHEMISTRY OF PIGMENTS. 

oxide is obtained. The process should be carried out in a 
covered porcelain or earthenware crucible at a dull red heat. 

4Hg2Cr04 = 2Cr.p3 + BHg + SOg. 

(b) Potassium bichromate is ignited with sulphur. Potas- 
sium sulphate and chromium oxide are left in the crucible 
and can be separated by washing. The following scheme 
may represent the action : — 

KgCraOY + S = K2SO4 + CrgO.. 

(c) Potassium chromate and charcoal are ignited together 
in a crucible. Potassium oxide and carbonate, and chromic 
oxide remain. 

The melt is treated with boiling water, and after disin- 
tegration, the liquid is boiled to precipitate any hydroxide of 
chromium which may have formed and dissolved in the free 
alkali, and the insoluble part, after washing, is dried and 
ignited. Chromium oxide prepared in this way is seldom 
free from alkali. 

(d) By the ignition of potassium bichromate with an 
•equal weight of ammonium chloride and a little sodium 
•carbonate a mixture of alkaline chloride and chromic oxide 
is obtained. 

(e) On the ignition of ammonium bichromate a violent 
action with incandescence takes place, and a voluminous 
green-tea-like residue of chromium oxide remains. 

By all the methods described above the green oxide of 
chromium CrgOg is obtained. Two other substances closely 
allied to it are, however, used as green colouring matters — a 
hydroxide and a phosphate of chromium. 

GuigneVs green, vividian (veridian), Mittler's green, chramium 

hydroxide, Cr^O^ 2H^0, 

This brilliant emerald green pigment is prepared by the 
ignition of three parts of boric acid with one part of potassium 



INORGANIC PIGMENTS. 115 

bichromate to dull redness for a suitable period. On the 
small scale we have found one hour sufficient. A copious 
evolution of oxygen and violent frothing take place ; it is 
therefore advisable to use a large crucible for the fusion. The 
melt is washed out with hot water, and if the operation has 
been carried out properly, only a very slight yellow colour 
should be imparted to the wash water, the whole of the 
chromate being reduced. It appears that a mixture of 
potassium and chromium borates is formed, and the latter is, 
on heating with water, decomposed and hydrolised into 
chromium hydroxide and boric acid. 

The product obtained by us in this manner was a full 
brilliant green, and after careful washing and drying, first in 
the air and then in a water oven, it lost on ignition 14*1 per 
cent. CrgOg 2H2O requires 19*0, CrgOg H2O 10-5. This sub- 
stance would appear to be a mixture. 

We found that by using less boric acid a dull green, 
which only lost a trace on ignition, and was evidently CrgOg, 
was obtained, and the action was by no means complete, a 
good deal of unaltered bichromate being present. This seems 
to point to the need of sufficient boric acid to form chromium 
borate in order that the hydroxide and not the oxide may be 
formed. 

A sample of Guignet's green, prepared by M. Kestner, 
and analysed by a Mr. Shipton, one of Hoffman's pupils, 
contained boric acid, and on drying at 100° had the following 
composition : — 

Oxide of chromium . . . 76*47 

Boric acid 1 12-10 

Water 11-43 



100-00 

A sample of " green oxide of chromium," sold by a firm 
of artists' colourmen of repute, was examined by us. It 
contained — 

^ By difference. 




116 CHEMISTRY OF PIGMENTS. 



Oil 


27-4 


Chromium oxide 


660 


Alumina . . . . 


5-6 


Lime salts, etc. 


1-0 



1000 

The proportion of alumina seems larger than might 
reasonably be present as impurity ; it was possibly added to 
reduce the colour to a standard tint. 

A sample of veridian examined by us, from the same maker 
as the green chromium oxide just noticed above, contained : — 

Oil (loss on ignition less HgO calculated) . 48*9 

Chromium hydroxide 46*4 

After iffnition / ^***®^ soluble in water (alkaline chromate) 3*5 

I Matter soluble in acid 1*2 



1000 

An actual determination of oil gave 50*3 per cent. This 
rather tends to show that our calculation of chromium 
hydroxide as CrgOg 2H2O from the percentage of CrgOg was 
not justified ; we suggest this in view of the composition of 
our own preparation. The unaltered chromate which, per- 
haps, would brighten the green seems to point to insufficient 
ignition and subsequent insufficient washings. Its presence 
is, in our opinion, undesirable. 

IVa— THE CHROMATE COLOURS. 

We believe we are correct in stating that all chromates 
are coloured bodies, but only certain of these compounds, 
from the beauty of their tint and other considerations, are 
used as pigments. Of these the principal are the chromates 
of lead, while less important members of the group are zinc, 
barium, and strontium chromates. 

The Chromates of Lead. 

Lead forms two definite compounds with chromic acid — 
the neutral chromate containing one equivalent of chromic 



INORGANIC PIGMENTS. 117 

anhydride and one of lead oxide (PbO), a yellow compound 
varying in depth of colour according to the conditions of its 
formation, and represented by the formula PbCrO^, and a 
basic chromate containing two equivalents of PbO to one of 
CrOg, PbgCrOg ( = PbCrO^, PbO), a beautiful red compound. 
An intermediate substance, probably a mixture, is known as 
orange chrome. 

Normal Lead Chromate Colours (Chrome Yellow, Paris 

Yellow, Cologne Yellow, etc.). 

When a neutral or only slightly acid solution of a lead 
salt is treated with a solution of a chromate a heavy yellow 
pulverulent precipitate separates, and an alkaline salt is left in 
solution. In the case of lead acetate and sodium chromate 
the changes occurring may be represented by the equation — 

Pb (C2H302)2 + Naa Cr04 = PbCr04 + 2NaC2H302. 

The compound thus produced is constant whatever the 
conditions of precipitation ; a full yellow, such as pure 
chromate, is not often used in commerce. Such pure colours 
are not, however, entirely unknown, one examined by us, 
ground in oil, had the composition — 

Oil 260 

Lead chromate (PbCrOJ .... 76-0 

100-0 

It is more common to prepare a diluted pigment contain- 
ing a greater or less percentage of some inert white sub- 
stance ; by this means a range of colours from a full orange 
yellow to the palest lemon can be obtained. 

There are three types of these diluted yellows, (a) chro- 
mate white lead yellows, {b) chromate lead sulphate yellows, 
(c) chromates diluted with whites not containing lead. 

(a) The first typQ of yellow, which seems, though not 
very much used, to be. theoretically the most satisfactory, 
having regard to the excellent drying and covering powers of 




118 CHEMISTRY OF PIGMENTS. 

white lead, is prepared by treating dry white lead with a 
quantity of dilute acetic or nitric acid insufficient to entirely 
dissolve it, and precipitating with alkaline chromate, or more 
usually bichromate, in insufficient quantity to attack all the 
dissolved lead. By this means a mixture of lead chromate 
and white lead is obtained, which varies in colour according 
to the amount of white lead dissolved. This is allowed to 
deposit, and washed free from soluble salts. 

Two samples, evidently prepared by this method, and 
called '*pure chrome yellow," were almost pure lead chro- 
mate of a full colour. 

Lead chromate 92*2 93*4 

White lead ..;... 7-8 6*6 

1000 100-0 

Samples of lemon and orange yellow of this kind had the 
following composition : — 

Lemon. Orange. 

Lead chromate 31*5 47*7 

White lead ...... 59*0 47 2 

Insoluble in acid 2*7 — 

DifEerence 6*8 6-1 

100-0 100-0 

(b) The second type of colours, with lead sulphate as a white 
base, is always considered by the trade as pure, consisting 
only of lead compounds. Colours of this kind are usually 
prepared by precipitating lead acetate or nitrate with mixtures 
of alkaline bichromate and Glauber's salts (sodium sulphate) 
or alkaline bichromate and sulphuric acid. Lead chromate 
and lead sulphate are by this process simultaneously pre- 
cipitated, and the proportions may be so adjusted as to 
produce the requisite variety of shades. 

Biot and Delisse precipitate lead sulphate by treating lead 
acetate with sulphuric acid or sodium sulphate, and then 
digest three parts of the washed precipitate with one part of 



INORGANIC PIGMENTS. 119 

potassium chromate in hot water. The conversion of the 
chromate according to the following scheme — 

KgCrO^ + PbS04 = PbCr04 + K2SO4, 

is almost complete, and the lead chromate is obtained mixed 
or combined with the unaltered lead sulphate. By this 
means a good yellow is produced of very high colour for the 
amount of chromate used ; the covering power is, however, 
less than that of the precipitated yellow. Lead chloride is 
converted iiito chromate in a similar manner. 
We have examined some of these colours : — 

. 50-4 
. 41-2 
. 8-4 



Lead chromate . . . 57*3 


Lead chromate 


Lead sulphate . . . 26-3 


Lead 


sulphate 


Calcium carbonate, etc. . 7*1 


White lead . 


Insoluble in acid (BaSOJ . 9*3 






100-0 






Oil ... 


• 


22-2 


Lead Chromate . 


• 


38 -8 


Lead sulphate 


• 


23-2 


Sulphate of lime . 


• 


15-8 



1000 



1000 

(c) The third class, comprising the cheaper chrome 
yellows of the kind usually known as Cologne yellow, includes 
all those colours where the required paleness of tint is 
obtained by the addition of white substances other than lead 
compounds, such as sulphate of barium. 

Basic Lead Chromates. 

The basic compounds (or rather, perhaps, mixtures of lead 
chromate) include orange chrome and chrome red, the latter 
being the more basic substance. 

These substances are usually prepared by the action of 
sodium hydroxide on yellow lead chromate, the alkali 
abstracting the chromic anhydride from a portion of the lead 
compound, forming alkaline chromate, while basic chromate^ 
of lead remains. 

2PbCr04 + 2NaOH = PbaCrO^ + NaaCrO^ + HaO. 



120 CHEMISTRY OF PIGMENTS. 

Basic lead chromate is known as Derby red or Chinese 
red. It is, when carefully prepared, a very beautiful colour, 
somewhat resembling vermilion. It is, sometimes at least, a 
crystalline substance consisting of single rectangular prisms, 
and it is stated that the brightest shades owe their beauty to 
the (relatively) large size of the crystals. It is desirable to 
make small, roughly quantitative experiments to ascertain 
the proportion of alkali and chromate required to prepare a 
pigment of the desired colour and to use the same proportions 
and dilution in the actual preparation. 

Liebig and Wohler prepared vermilion-coloured reds by 
dropping into a fusion of equal weights of potassium and 
sodium nitrates, small pieces of chrome yellow. Ebullition 
occurs and the mass becomes black ; it is heated until ebulli- 
tion ceases. If it is overheated the product becomes brown 
(? owing to formation of lead dioxide). The melt should be 
washed quickly. 

Another process is to treat a solution of lead acetate with 
a mixture of potassium hydroxide and chromate. 

2Pb02(C2H30)2 + 2K0H + KgCrO^ 
= PbaCrOj + dKO'CgHp + OHj. 

Prinvolt prepared a chrome red he called Persian red by 
digesting 25 parts of lead carbonate with 10 parts of potas- 
sium chromate dissolved in water, for two days. Basic lead 
chromate and potassium bichromate (and carbonate) are said 
to be formed. The liquid is boiled for half an hour, some of 
the precipitate becomes decomposed and lead chromate is 
formed, the precipitate turning violet. This is washed and 
digested with sulphuric acid (1 in 100 water) and the red 
pigment is the result. 

We have examined several samples of Derby red, Chinese 
red and orange chrome, of which we give the composition. 



INORGANIC PIGMENTS. 121 

Chinese Bed. Derby Red. 

Water and volatile matter — — — 0*7 — — 

Lead oxide (PbO) . . 800 80-1 .79-8 79-2 79-3 80*8 

Chromic anhydride . 16-8 17*2 17*8 18-1 17-6 17*6 

Other matters ... 32 27 *2-4 2-0 3-2 *1*6 

1000 1000 1000 1000 100-0 1000 

Orange Chrome. 

Lead oxide. . . . 79-4 80-4 74*6 72-7 

Chromic anhydride . . 14-3 129 13*9 147 

Other matters ... 6-3 67 11*6 12*6 

COg 100-0 1000 100-0 1000 

In most of the above samples the '* other matters" con- 
sisted of carbonate of lime, which in small quantity is 
easily accounted for by the action of alkali on hard water 
used in manufacture thus: — 

CaCOj, HaCO, -t- 2K0H = CaCO. + K3CO3 

+ H2O' 

The samples marked* were also brightened with eosin 
(about 0*3 per cent.), which is an undesirable practice. 

One sample of Derby red examined by us was not a 
chrome colour at all. It had the following composition : — 

Water 8-5 

Loss on ignition 4-0 

Ferric oxide 15-9 

Alumina 1-1 

Sulphate of lime 42*3 

Carbonate of lime 3-9 

Insoluble siliceous matter .... 24-3 

• 

100-0 

— a similar pigment to the colour known as light red, 
which is very much cheaper than a lead chromate. 

Zinc Chromate (ZnCrOj. 

This pigment is prepared by precipitating a solution of 
zinc sulphate with a solution of sodium or potassium chro- 
mate. It is necessary that the zinc salt should be fairly pure 



A 



122 CHEMISTRY OF PIGMENTS. 

and should be treated with sodium hydroxide or carbonatev 
which precipitates a small amount of zinc hydroxide or car- 
bonate. The precipitate which is formed on the addition of 
alkaline chromate is of a pale yellow colour, and only requires, 
washing, drying and grinding to render it suitable for use. 

E. Wagner gives the result of the examination of sam.ple& 
of English and German manufacture : — 

ENGLISH. 

ZnCr04^ 

Chromic anhydride .... 14'94 55*2 

Zinc oxide 76-35 44-8 

Carbon dioxide 3 "61 — 

Water 6-19 ^ — 

10009 1000 



GERMAN. 

Chromic anhydride . . . 11-88 9-21 

Zinc oxide 4578 61-47 

Barium sulphate .... 42-34 29-32 



100-00 10000 



It will be seen that the use of barium sulphate for '' lower- 
ing*' purposes is not an exclusively Enghsh custom. All 
these colours have evidently been prepared by previous pre- 
cipitation of oxide or carbonate as there is but a very small 
proportion of CrOg present in any of the three. 

Zinc chromate is, we believe, only used to a very small 
extent in commerce. We have never yet examined a sample 
of this pigment. 

Silver Chromate (Ag^jCrOJ. 

This blood-red pigment, prepared by the precipitation of 
neutral solutions of silver nitrate with alkaline chromates, 
is said to be used to some extent in miniature painting. It is 
unnecessary to state that it is a very expensive substance, and. 



INORGANIC PIGMENTS. 123 

whatever its merits, only suitable for use on the very small 
scale. 

Mercury Chromates. 

Mercurous chromate, Hg'2Cr04, prepared in a similar man- 
ner to silver chromate, has been used as a pigment. It is 
both costly and easily decomposed by light. It is of a brick- 
red colour. 

Mercuric chromate, Hg"Cr04, prepared by the precipitation 
of a mercuric solution with alkaline chromate, is a light-red 
pigment. 

We believe neither of these substances has ever been used 
to any extent as a pigment, nor are they suitable. For the 
analyses of the chromates of lead and mixed colours contain- 
ing these compounds the following scheme will be found 
satisfactory : A suitable quantity (about 1 gram) of the 
oil-free colour is weighed into a beaker, covered with hydro- 
chloric acid, and the beaker, covered with a watch-glass, 
placed in the waterbath to digest for fifteen to thirty minutes. 
At the end of this time the chromate will have been reduced 
to chromium salt in accordance with the scheme — 

Cr03 + 6HC1 = CrClj + 3H2O + 3C1. 

The liquid is now diluted with boiling water. The cover and 
the sides of the beaker are washed to prevent loss of spray 
and the beaker heated on a flame, with stirring. If any in- 
soluble matter remains it should be well washed with hot 
water and its nature examined. It is most likely to be either 
barium or lead sulphate, though the latter would be partly 
dissolved by hydrochloric acid. The mixed filtrate and wash- 
ings are treated with sulphuretted hydrogen (after dilution and 
cooling) and the sulphide of lead collected and treated as de- 
scribed on page 93 (white lead). The excess of H2S is removed 
from the filtrate by boiling, a few drops of nitric acid added 
to oxidise any iron, if present, and ammonium hydroxide 



124 CHEMISTRY OF PIGMENTS. 

solution added. This precipitates chromium hydroxide, which 
is collected, washed, ignited (still in the filter paper) in a pla- 
tinum crucible and weighed as CraOg. If a preliminary test 
has indicated the presence of iron this would also be included 
in this precipitate as FegOg and should be estimated by titra- 
tion, after reduction with SnClg, with bichromate. Barium 
or lime would be found in the filtrate from the " ammonia 
precipitate," which, in this as in all other cas.es, should after 
the first precipitation be washed by decantation partly on to 
the filter, given one or two washings, and then the contents 
of the filter washed into the beaker used for precipitating, 
redissolved in HCl, and reprecipitated by ammonia which 
should be only added in slight excess, the excess being boiled 
off. Unless this procedure is adopted lime is always likely to 
be precipitated with the bases of the chromium group. Lime 
can be determined in the mixed filtrates by precipitation with 
ammonium oxalate and conversion to carbonate or oxide > 
barium would also be precipitated by ammonium oxalate, 
hence it would be well to dissolve the carbonate or oxide 
when weighed in a large excess in fairly strong HCl, and add 
sulphuric acid to the hot solution. Under these conditions 
barium sulphate would be precipitated and calcium sulphate 
remain in solution. It is, of course, impossible that barium 
should be present in solution if a preliminary test on the 
original pigment indicated the presence of sulphates soluble 
in hydrochloric acid. If these be present the SO3 should be 
determined in a fresh portion of the pigment treated with 
HCl, as already described, by precipitation with barium 
chloride. Lead sulphate, though almost insoluble in water, 
is moderately soluble in a large volume of hot HCl. 

Having determined the amounts of lead, chromic acid 
(CrgOg corresponds to 2Cr03), lime, barium and sulphuric 
anhydride, if present, it now remains to combine these as they 
really existed in the pigment. If the lead oxide is in excess of 



INORGANIC PIGMENTS. 125 

that required for PbCr04, and the colour of the pigment does 
not indicate the presence of basic chromate, and SO3 is absent, 
it is best to consider the excess as white lead. Lime would 
be present as sulphate or carbonate, barium as chromate or, 
if in the insoluble matter, as sulphate. If sulphuric acid is 
present, and more lead present than required for all the CrOj, 
then the SO3 should be calculated to PbS04, and if this agrees 
fairly well with the excess of lead, returned as such, but of 
course some judgment is required to decide such points. In 
the case of obviously basic chrpmates it is best to return PbO 
and CrOg together with such impurities as may be present. 

In all cases it is a good plan to determine whether boiling 
water extracts more than traces of alkaline and other soluble 
salts, for the presence of these in any quantity is due to careless 
washing. A sufficiently accurate method for the examination 
of lead chromate colours is to treat a weighed quantity with 
HCl, evaporate to dryness and wash with alcohol. Chromium 
chloride and any chloride of calcium or other probable metals 
are dissolved, leaving lead chloride, which is insoluble in 
alcohol and can be weighed. The chromium can be deter- 
mined in the filtrate, after evaporating oflf the alcohol, by 
precipitation with ammonia, and is weighed as CrgOg. Cal- 
cium can be determined in the filtrate from the ammonia 
precipitate. If SO3 is present, a mixture of PbSO^ and PbCl^ 
wiU be left insoluble in alcohol, and a determination of the 
SO3 in a separate portion of the pigment should give figures 
for calculating the actual amount of lead in the mixed 
sulphate and chloride. 

This method we have found more especially useful in the 
case of chrome red and orange, which are usually fairly pure. 
Its advantage is that the use of HgS is not necessary, an 
advantage in a laboratory which is not isolated from the rest 
of the world. 

The percentage of CrOg in cbromates may be determined 



126 CHEMISTRY OF PIGMENTS. 

by passing the chlorine evolved on treatment with HCl, into 
potassium iodide solution, and titration of the liberated iodine 
with sodium thiosulphate — 

R"Cr04 + 8HC1 = WVl^ + CrClg + 3C1 + 4H2O 
KI + CI = KCl + I. 

Brunswick Green. 

This pigment is now a mixed colour, prepared by ad- 
mixture of Prussian blue with lead chromate, a suitable 
white diluent (usually barytes) being added in sufficient 
proportion to produce a manageable pignaent. It is a rather 
dullish pure green, and under ordinary conditions is fairly 
permanent, though chrome yellow has some action, in course 
of time, on Prussian blue. Brunswick green is very largely 
used for outdoor work, as painting ornamental ironwork, 
bridges, railings, gates, etc. 

There are two general methods of preparing this green, 
(a) by mixing the constituents ready formed, (b) by pre- 
cipitating the blue and yellow on the finely ground barytes. 

The composition of samples of light, middle and dark 
Brunswick green examined by us is given in the following 
table : — 

Light. Middle. Dark. 

Chrome yellow (PbCrOJ .... 5-59 1-16 10-11 

Prussian blue 0-95 0-66 4*96 

Barium sulphate 91-74 90*39 79*40 

Lime, salts, etc. . . . . . 1-72 7*79 6*53 

100 00 100-00 100-00 

The following paragraphs from the paper on Prussian 
blue published by us {Analyst, 225, 1896) sufficiently describe 
the method of analysis found by us to be satisfactory : — 

*'Two samples of Brunswick green ground in oil were 
examined. Brunswick green is a Prussian blue-lead chromate 
green mixed with barium sulphate (' barytes '). A portion 
from which the oil had been extracted was gently ignited 



11-27 


13-55 


101 


4-21 


4-98 


710 


82-74 


75-14 



INORGANIC PIGMENTS. 127 

and treated with hydrochloric acid, the solution of lead, iron 
and chromium chlorides filtered from the barium sulphate, 
and the lead precipitated with sulphuric acid. In the filtrate 
from the lead sulphate the 'ammonia precipitate ' containing 
the mixed oxides of iron and chromium was determined. 
The oxides were separated by fusion with alkahne carbonate 
and nitrate and extraction of the fused mass with water, 
PcgOg being insoluble. Direct titration with KgCrgO^ was 
•difficult, as the colour of the chromium masked the reduction 
of the iron with stannous chloride : — 

Light Green. Dark Green. 

Oil 

Prussian blue (Fe x 3-03) . 

Chrome yellow . . 

Barium sulphate .... 

10000 100-00 

** The nitrogen was determined in each of these samples 
in about 5 grams, and was '19 and 72 respectively, which, 
using 4"4 as a multiplier, would give '83 and 3*16 per cent, 
of Prussian blue in these samples. We are much more 
inclined to rely on a direct determination of this kind than 
on the determination of the iron by the method described. 
The method of analysis for these colours described by Hurst, 
and due to Brown {Chem. News, 31st December, 1886), seems 
still more unsatisfactory. The green is treated with hydro- 
chloric acid to dissolve out the lead chromate (of course, as 
lead and chromium chlorides). The residue, barytes and 
Prussian blue, is ignited to decompose the blue, weighed, 
treated with aqtta regia to dissolve out oxide of iron (and 
alkalies), and the insoluble portion again weighed. The 
diflference is to be taken as oxide of iron, and multiplied 
by 2*212 to give Prussian blue. The lead and chromium 
are of course determined in the original filtrate." 



128 CHEMISTRY OF PIGMENTS. 

v.— IRON OXIDE PIGMENTS. 

A most important class of colours, on account both of 
their very general use, extending to remote antiquity, and of 
their high intrinsic value, is that array of pigments the 
colours of which are due to oxide and hydroxide of iron. 
This class comprises both natural and artificial colours of 
varied shades of yellow, red, brown and purple ; of the 
natural earths some are darkened in colour by roasting, 
resulting in the loss of water of hydration and consequent 
formation of a redder oxide ; most or all, however, of the 
natural earths are also used in their unburnt state. 

The composition of these colours is very variable ; some 
of the red and purple pigments are nearly pure ferric oxide 
(FegOg), others contain large amounts of silica and lime salts, 
whilst not infrequently barium sulphate is found as a natural 
admixture ; many of the browns owe their rich colour to 
the presence of small quantities of oxide of manganese ; of 
the yellows, most are hydrated oxides and silicates of iron, 
usually considerably diluted by (natural) admixture with lime 
salts. 

In considering this group of pigments we propose to 
give brief descriptions, first, of the natural earths, raw and 
*' burnt," and then of those members of the group which are 
usually prepared by more artificial means. It will be con- 
venient to consider the general properties and method of 
analysis of these colours as a group rather than as individuals. 

• 

The Ochres. 

There are two distinct series of <3olours known under the 
name of ochres, namely, those which owe their colour to 
hydrateS oxide of iron — the yellow and brown ochres, and 
those which are coloured by the anhydrous oxide — red ochres. 
Members of the former class, by the simple process of roast- 



INORGANIC PIGMENTS. 129 

ing (and consequent dehydration), are converted into the 
latter. 

The ochres essentially consist of ferric hydroxide or oxide, 
which is usually more or less mixed with clay, sand, lime 
salts, and occasionally magnesia. The most used ochres are 
those known collectively as yellow ochres. Yellow ochre is 
the &'XpcL known to the Greeks in the time of Apelles, used 
also by the Egyptians and Romans, and also by savage 
nations in later times for painting their bodies. Its colour 
is due to yellow haematite, xanthosiderite, FcgOg, HgO, brown 
haematite, liinonite, 2Fe203, H2O, and bog-iron ore, lymnite, 
Fe^jOg SHgO ; the brown haematite, according to Church, 
being the most commonly occurring. 

In England ochres are found in Cornwall, often associated 
with tin and copper ore and separated from these by elutria- 
tion, in Derbyshire and at Shotover Hill in Oxfordshire, not 
to mention other localities. The beds are usually above the 
oolite deposit, covered by sandstone and quartzose sands 
more or less ferruginous, with plastic clays also containing 
iron. The following sectional measurements of the Shot- 
over deposit are taken from Dr. Ure's dictionary: — 

Ferruginous grit (forming summit of hill) . . 6 feet 

Grey sand 3 

Ferruginous concretions 1 

Yellow sand 6 



Cream-coloured loam 4 



Ochre 6 inches 

A further deposit of ochre occurs beneath a layer of clay. 
A sample of this Oxfordshire ochre examined by Prof. 
Church contained : — 

Hygroscopic moisture 7*1 

Combined water 9*0 

Ferric oxide 13-2 

Alumina 6*3 

Silica 61-5 

Calcium sulphate 1*4 

Undetermined 1*6 

100-0 

9 



130 CHEMISTRY OF PIGMENTS. 

A sample called Oxford ochre examined by us gave the 
following figures : — 

Oil and water of combination 81 *32 

Oxide of iron 9*04 

Alumina 5"13 

Lime salts 5'20 

Insoluble matter ^ 49 '31 



100 00 
* Including barytes (BaSOJ 20*62 per cent. 

This differs from Church's sample in containing barytes. 
Though native ochres are very largely used in England, 
India, France, Italy, Spain and Germany also supply us 
with considerable amounts of this valuable pigment. The 
composition of some of these is given below. 

Yellow ochre varies considerably in colour, the variation 
being caused by the presence of different hydroxides of 
iron and varying amounts of white matter (clay, etc.). It is 
seldom that the clay contained in ochre is very ferruginous, 
samples usually leave a fairly white residue on treatment 
with strong hydrochloric acid. The colour varies from a 
pale dull yellow to that now known in England, as it had 
for years been in India, as khaki. 

Yellow ochre, being a cheap pigment, is not much subject 
to adulteration ; barium sulphate is sometimes present, but 
it is difficult to decide whether this is not naturally occur- 
ring, and, in any case, if the tint is suitable, its presence is 
entirely harmless. Church states that occasionally ochres 
are brightened by the addition of such organic colours as 
turmeric. In this case a yellow colour would be imparted 
to alcohol, or, if the pigment were ground in oil, probably 
a mixture of alcohol and ether would extract both colour 
and oil, and the addition of alkali would, by causing change 
of colour, indicate the presence of turmeric. 



INOEGANIC PIGMENTS. 



131 



Brown ochre is very similar to raw sienna, which is 
also dealt with in this chapter. 

An analysis of brown ochre sold by a firm of artists' 
colourmen of repute gave the following figm^es : — 



Oil .... 
Water of hydration, etc. 
Ferric oxide . 
Alumina 
Lime salts, etc. 
Insoluble siliceous matter 



I- 39-0 

34-6 
4-7 
6-6 

15-1 

1000 



The following analysis of a New Zealand ochre, used 
as a paint by the natives, given in Dundas Thomson's 
Cyclopcedia of Chemistry, is of interest : — 



Ferric oxide 
Silica . 
Water . 
Organic matter 



64-36 
13-92 
20-2 
4-72 

103-20 



This contained traces of alumina and lime, and gelatinised 
with acids. The colour of this ochre is not stated. 

COMPOSITION OF YELLOW OCHRES. 





French French 
Ochre. Ochre. 


stone 
Ochrc* 


" Yellow 
Ochre." 


stone Stone 
Ochre* Ochre.* 


Stone 
Ochre. * 


Water . 
Loss on ignition 


SI « 


127-8 


1-70 
4-15 


38-31 23-37 


23-72 


Oxide of iron . 
Alumina . 


IS} »'» 


(11-2 
"1 4-6 


13-95 


43-64 24-75 


22-31 


Lime salts, etc. 


•64 


1-2 


3-20 


8-05 3-28 


0-68 


Insoluble in HCl . 


69-50 56-63 


55-2 


77-00 
100-00 


10-00 48-60 


53-09 




100-00 100-00 


1000 


100-00 10000 


100-CO 


Barium sulphate . 






— 38-62 


61-05 




* Stone Ochre. 








Oil 


• • • 






24-5 




Water ot combination . 






3-3 




Oxide of 


iron 






11-2 




Alumina 


... 






4-6 




Lime salts, etc. . 






1-2 




Insoluble siliceous mattei 






55-2 





100-0 




132 CHEMISTKY OF PIGMENTS. 

The variation in composition of these samples, of which 
those marked with an asterisk (*) were. ground in oil, is 
very remarkable considering that the variation of tint is 
not great. The large amounts of barium sulphate present 
in some of these may be naturally occurring, but have prob- 
ably been added to a natural earth of full colour which 
would bear lowering. The variations in the amount of ferric 
oxide, or rather hydroxide, are equally remarkable. 

Bed ochre was also known to the Greek painters, who 
obtained it from Cappadocia and called it sinopis ; it was also 
known as rubrica, and now goes under a variety of names as 
red haematite, ruddle, reddle, red chalk, bole, red-iron ore, 
scarlet ochre, siniped miltos, terra rosa. Its colour is due 
to anhydrous ferric oxide. A very remarkable feature about 
this and other red oxide paints is the fact that the propor- 
tion of ferric oxide is no indication of the depth of colour, 
■or, rather, affords but slight indication. Church quotes a 
haematite from Cumberland which gave — 

Ferric oxide 94*7 

Alumina 2*0 

Silica 2-2 

Moisture . 1-1 

100-0 

Other " almost equally rich red ochres contain much less 
iron oxide, a sinopis from Anatoha, analysed by Klaproth, 
having been found to contain 21 per cent, only, and others 
from other localities not above 40 ". 

Four samples of Cornish ochres were examined by us 
with the following results : — 

Ferric oxide .... 40*2 52-3 68-0 85-9 

Manganese dioxide ... 0-8 1-2 1-4 0*6 

Lime salts, etc 4-4 4-6 6-2 4-1 

Siliceous matter . . . 54*6 41*9 24-4 94 

100-0 100-0 1000 100-0 



INORGANIC PIGMENTS. 



133 



These were of a fine colour, but those containing more 
than traces of manganese were somewhat of a reddish-brown 
tinge instead of pure red. 

Closely allied to red ochre are genuine Indian red and 
Venetian red. 

Indian Red should be a natural iron ore or haematite con- 
taining over 90 per cent, of ferric oxide, and of a rich purplish- 
red colour. Some of the red imported from India is obtained 
by roasting lighter-coloured ores, but most specimens are 
really natural ores. Church states that some is imported 
from Ormuz in the Persian Gulf, and that some is an EngUsh 
haematite from the Forest of Dean. The principal feature, 
from the colour point of view, of this pigment is the slight 
purplish tint it possesses. 

Indian red as sold is often an admixture of iron oxide with 
other materials, probably the result of judicious blending of 
purple brown, red ochre or " Ught red," and cheap white 
substances. We give below the composition of samples of 
the pigment, both in the dry state and ground in oil, which 
have been examined by us : — 





L 


II. 


ni. 


IV. 


v. 


VL 


Loss on ignition 


— 


22-29 




30-12 


0-75 


14-00 


Oxide of iron 


94-00 


71-34 


96-07 


61-92 


59-281 
115 


53-75 


Alumina 

Lime salts, etc. . 


1-88 \ 
3-42J 


5-26 


3-88 


6-34 


28-21 


Insoluble in H Gl . 


0-70 


1-11 


0-05 


1-62 


38-82» 


404 



100-00 100-00 10000 100-00 100-00 10000 
^ 35-82 per cent. BaSO^. 

The two latter samples certainly were not entitled to the 
name of Indian red, but the others, of which II. and IV. were 
ground in oil, would appear to be genuine. The adulterated 
samples seldom have the soft appearance of the genuine 
Indian red. 

Venetian Eed (Rouge, crocus, colcothar, caput mortuum 



134 CHEMISTRY OF PIGMENTS. 

vitrioli) originally was a similar produce to Indian red, but of 
a purer red tone. Of late years various artificially calcined 
iron oxides and mixed colour^ — diluted ferric oxides — have 
been sold under this name. 

The following three samples sold as Venetian red were 
very satisfactory colours, but could hardly be described as 
haematites, or even as calcined iron oxides : — 

Loss on ignition . . . . 1-50 (including oil) 19 "49 

Oxide of iron 21-75 17-20 



Alumina 6-00 2-11 



} 



24-42 



Calcium salts, etc 11-56 64*94 13-20 

Insoluble in hydrochloric acid ^ . 60-19 15 75 42-89 



10000 100 00 10000 • 

^ This was barium sulphate. 

We find, in fact, on looking over many analyses, that we 
have not, in the case of pigments used on the large scale, 
come across one sample which could be justly termed a 
haematite. 

Judging from one of its early names, caput mortuum 
vitrioli, it would appear that calcined green vitriol, or ferrous 
sulphate, the residue (caput mortuam of the alchemists) of 
the preparation of Nordhausen sulphuric acid, was recognised 
as a substitute for the true red earth sold in Venice, or, 
probably, used by the Venetian school of painters. 

Artificial oxides obtained in this and other ways will be 
considered in a later section of this chapter. 

Siennas and Umbers. 

These beautiful yellow and brown earths, doubtless, 
originally took their name from the localities in which they 
were first found. The existence at Sienna and Umbria of 
early schools of painters naturally led to the search for 
suitable colours, and in the ferruginous clay of these districts 
useful colours were found. The terms now have a more 



INORGANIC PIGMENTS. 



135 



extended use, and are applied to any earths having the same 
general properties as those found in Sienna and Umbria. A 
very valued variety of umber, for instance, comes from 
Cyprus, and is known as Turkey umber. 

Raw Sienna is usually a marl, occasionally a pure, or 
nearly pure, clay, containing a considerable proportion of 
ferric hydroxide, or rather, perhaps, hydrated ferric silicate. 
It is a rather transparent colour, and works well in both 
water and oil. Its usual tint is a dullish yellow or yellowish- 
brown, somewhat like the real khaki. Its permanence under 
all ordinarily possible conditions is absolute. 

We give below the composition of some samples of this 
pigment, both in the dry state and ground in water and oil, 
which have been examined by us : — 



DRY SIENNA. 






Hygroscopic water 






4-94 


Water of combination . 


11-7 


9-30 


2-34 


Oxide of iron 


1 361 
33-1 ) 


30-72 


30-18 


Alumina .... 
Lime salts .... 


38-83 


4-65 
35-64 


Insoluble siliceous matter 


191 


21-15 


22-25 




100-0 


10000 


10000 


SIENNA OR 


OUND IN WATER. 






Water. ... 
Water of combination 


44-70) 
. 3-90 [ ^^'^ 


42-27 
3-28 


47-59 
3-09 


Oxide of iron 

Alumina .... 

Lime salts .... 


' |- 20-44 25-29 
17-58 21-05 )■ 


18-80 
24-30 


16-02 

2-64 

19-02 


Insoluble siliceous matter . 


13-33 9-00 


11-35 


1164 




100-00 100-00 


100-00 


100-00 


RAW SIENNA 


L GROUND IN OIL. 






Oil, water of hydration, etc. 


40-61 43-12 64-15 


34-39 


24-3 


Oxide of iron . . A 
Alumina . . . ./ 
Lime salts .... 


27-89 25-73 31-63 
18-98 18-11 6-29 


14-20 
1 25-07 


30-3 
7-3 
2-9 


Insoluble siliceous matter . 


12-52 1304 7-93 


26-34 


35-2 



100-00 100-00 100-00 100-00 100-0 



136 CHEMISTEY OF PIGMENTS. 

It will be noticed that, speaking generally, the proportion 
of siliceous matter is much lower in these earths than in the 
ochres. Those ochres which contain only a small amount' 
of silica are usually of a deeper, browner shade, more ap- 
proaching these colours. In fact, the difference between 
yellow ochre and raw sienna would appear to be rather one 
of locality and depth of tint than of constitution, of degree 
rather than kind. 

Btjbnt Sienna is, or should be, obtained by carefully cal- 
cining raw sienna, until, by the expulsion of a portion or the 
whole of the water of combination, a rich reddish-brown 
pigment is obtained. This, like raw sienna, works well in 
both oil and water, and from its pleasing colour and great 
permanency is held in considerable esteem. Judging from 
the composition of some samples we have examined, we 
think it probable that any ferruginous earth of the requisite 
reddish-brown shade is sold as burnt sienna. This substitu- 
tion cannot altogether be regarded as fraudulent, as it is 
difficult to see in what way the buyer is injured, provided the 
tint is right and permanent. 

The small amount of lime in some of these siennas is 
very remarkable, and rather tends to support the opinion 
expressed above as to substitution of any suitably coloured 
earth. 

We give the composition of samples of this pigment 
examined by us : — 

BURNT SIENNA GROUND IN WATER. 

Water (loss at 100°) 43-80 47-59 

Water of combination .... 2*47 1'69 

Oxide of iron 30*42 25*69 

Alumina \ „.qq 4*92 

Lime salts / 7*07 

Insoluble siliceous matter .... 15*41 13*14 



100-00 100-00 



INORGANIC PIGMENTS. 137 

BURNT SIENNA GROUND IN OIL. 

Oil 41-08 50-07 37-9 56*6 

Water of combination, etc. . . — — 3-7 7*8 

Oxide of iron 22-83 29*47 11-9 22-6 

Alumina l 4-83 0*7 1*3 

Lime salts ) ^*^* 1-84 0-6 — 

Insoluble siliceous matter . 25-75 13-79 7*8 12*6 

Barium Sulphate ..... — — 37-4 — 

100-00 100-00 100-0 . 100-8 

Raw Umber {Levant imiher, Turkey umber. Terra 'Omhrey 
umbraun, umbra, Kolnische Erde, Terra Ombra), — This brown 
earth, most of which comes from Cyprus, owes its olive brown 
colour, in which it differs from most of the iron colours, to 
the presence of a considerable quantity of oxides of man- 
ganese. An analysis by Church of a choice sample of 
C)rprus umber will indicate the general character of this 
pigment : — 

Water given off at 100° C 4-8 

Water given off at a red heat 8-8 

Iron oxide 48-5 

Manganese dioxide 19*0 

Lime 1-4 

Magnesia 0*5 

Alumina 2*1 

Phosphoric acid 0-9 

Silica 13*7 

Carbonic acid, etc 0*3 

1000 

Prof. Church remarks that ** this sample had the peculiar 
greenish hue so much prized by artists," and that '*it should 
be stated that a part of the manganese probably existed as 

The pigment is prepared by levigation, and subsequent 
drying at a temperature not much exceeding 100° C. If this 
is exceeded, not only will the hygroscopic moisture be 
expelled, but some of the water of combination, and a more 
or less burnt umber will result. 



138 CHEMISTRY OF PIGMENTS. 

Eaw umber is a very valuable pigment, as its colour is 
not easy to satisfactorily imitate, and it is under all ordinary 
conditions quite permanent : any changes in colour are more 
probably due to yellowing of the oil used as a vehicle than to 
alteration in the colour itself ; slight changes are also occa- 
sionally noticed in water colour, probably attributable to the 
use of a slightly bituminous earth, but in neither case is the 
change serious. 

We give below the composition of samples of raw umber 
obtained from various sources and examined by us : — 





I. 
High class 
artists' colour 
in oil. 


II. 

Oil- 
free 
Matter 
of I. 


III. IV. 

Turkey English 
Umber. Umber. 


V. 

Pre- 
pared 
Umber 


Oil ... . 


. 47-6 










Moisture 

Water of combination 


;[7-7 


14-6 


4-3 
6-9 


12-6 
8-3 


5-2 
11-0 


Ferric oxide 


. 18-6 


351 


44-9 


47-1 


50-4' 


Manganese dioxide 


. 11-2 


21-3 


14-0 


10-5 


13-8 


Alumina 


. 1-8 


3-4 


6-8 


31 




Lime salts, etc. . 


. 4-5 


9-1 


4-8 


3-0 


3-6' 


Insoluble siliceous matter 8-7 


16-5 


19-3 


15-4 


16-0 



FejO., & AI2 O3 
not separated 



100-0 100-0 1000 1000 100-0 

The percentage of manganese is, it will be noted, highest 
in the artists' colour and lowest in the English umber. We 
are not aware what process the prepared umber had passed 
through, but judging from its composition and colour we feel 
justified in stating that it had not been ignited (** burnt "). 

Burnt Umber, as its name implies, is obtained by calcin- 
ing the earth known as raw umber. It is slightly redder and 
darker than the unburnt earth, the change being due to some 
alteration in the hydration and constitution of the oxides of 
iron and manganese present. Prof. Church justly remarks 
that if the iron were present in umber to any considerable 
extent as ordinary hydroxides a much redder product should 
be obtained on calcination than is actually the case. Burnt 
umber is more translucent than the raw earth, and is to all 



INORGANIC PIGMENTS. 139 

intents and purposes absolutely permanent and inert to other 
pigments. 

We give some analytical figures which will sufficiently 
indicate the composition of this colour : — 

Burnt Turkey Umber. Burnt Umber. 

Moisture 2*6 6*00 

Water of combination, etc. . . . 4*2 — 

Ferric oxide 46-9 46-60 

Oxide of manganese 15*6 9*40 

Alumina 2*5 — * 

Lime salts, etc 3*8 16-86 

Insoluble siliceous matter .... 26*5 21-25 

1000 100-00 

^ Included with the ferric oxide. 

BURNT UMBER IN OIL. 

Burnt Turkey 
Umber. 

Oil ....... \ 

Water of combination, etc. . . J 

Perric oxide 22-8 26*7 18-6 * 

Oxide of manganese ... 4-3 9-0 6-8 

Alumina 3*9 3*4 1-3 

Lime salts ..... 11-2 3-4 0-3 

Insoluble siliceous matter ^ . . 18*1 12-4 40 2 

1000 1000 100-0 

^ And BaS04 10*5 per cent., 2-6 per cent., 30*4 per cent. 

The samples poor in manganese and containing barium 
sulphate in quantity were probably not genuine Turkey umber, 
but of English or Continental origin. They are seldom as 
fine in colour as the real Turkey (Cyprus) earth and are not 
by any means as costly or highly esteemed. 

Light Eei>, a colour more in use for artistic than for utili- 
tarian purposes, is, when genuine, a prepared ochre, a roasted 
yellow ochre. It is usually lighter and brighter than red 
ochre; Church well defines its colour as scarlet, modified 
by a little yellow and grey. 

The colour of light red is obviously due to anhydrous 



140 CHEMISTRY OF PIGMENTS. 

ferric oxide, and to obtain a good colour an ochre free from 
organic matter, which is not easy to burn off without heat- 
ing beyond the temperature required for a bright red, and 
one not too rich in hme, should be used. The temperature of 
roasting should not be too high ; a dull, red heat is sufficient. 
It must be remembered that ferric oxide colours look very 
much darker when hot than after cooling. The product is 
thrown into cold water, ground and washed. 

Light red is used in both oil and water-colour painting, 
and is quite permanent. We give the composition of two 
samples of this pigment ground in oil and sold by artists' 
colourmen of repute, examined by us : — 



Oil 

Water of combination . 
Ferric oxide 

Alumina . . . . 
Lime salts, etc. . 
Barium sulphate. 
Insoluble siliceous matter . 



I. 


II. 


j-61-6 


43-9 


6-0 


22-8 


8-8 


5-7 


2-6 


1-0 


3-6 


— 


32-6 


26-6 


1000 


100-0 



The difference in the percentage of ferric oxide is very 
remarkable, and, as the colours were of very similar tint, 
shows how little colour depends on the amount of iron and 
how much on its condition. Both samples might have been 
and probably were obtained by calcining natural earths, the 
small amount of barium sulphate present in I. being present 
either as a natural or accidental ingredient of the earth, or 
possibly added to reduce the pigment to a standard tint. 

Cappagh Brown (Euchrome — Mineral Brovm). — This brown 
earth, which in most respects resembles umber but is more 
reddish, is found in the Cappagh mines on the estate of Lord 
Audley near Skibbereen in Co. Cork. It gives off a good deal 
of water at 100° and contains only traces of organic matter. 
An analysis by Church is given below : — 



INORGANIC PIGMENTS. 141 

Water, given off at 100° C. ..'... 18-7 

Water, given off at a red heat 11 "6 

Ferric oxide (Fe^Os) 34-4 

Manganese dioxide (MnOg) 27*2 

Alumina 2*6 

Lime 1*1 

Magnesia trace 

Silica 4-6 

Phosphoric acid 0*4 

100-6 

Prof. Church states that probably some of the man- 
ganese exists as red oxide (Mn304) and also, very sensibly, 
suggests that *'the large quantity of water present in this 
mineral in a loosely attached form (hygroscopic), amounting 
to nearly one-fifth of the weight of the pigment indicates the 
the desirability of cautiously drying the substance previous to 
grinding it in oil. A temperature of 60° C. should not be 
exceeded." 

Cappagh brown works well in oil, particularly if dried as 
suggested. Church found that it became slightly redder on 
exposure for one month to light, but the change did not 
appear to increase after a further five months' exposure. 

Red Oxide (Chocolate, Purple Brown, etc.). 

For roagh outdoor work, the protection of ironwork and 
other purposes where it is desirable to obtain a cheap protec- 
tive coating rather than a particularly rich or delicate colour, 
coarse natural oxides are ground first roughly and then to a 
fine powder and used, ground in oil, under the name of red 
oxide, red oxide of iron, oxide, chocolate, etc. Those called 
red oxide of iron are usually fairly pure, but the others fre- 
quently contain considerable quantities of barium sulphate, 
sometimes natural, sometimes added. The colours of these 
oxides vary from a dark chocolate to a dull brickish red. 

These natural oxides and their artificial allies are very 



/ 



/ 



142 CHEMISTRY OF PIGMENTS. 

much used for painting bridges, girders and all sorts of iron 
structures. So long as the oil with which these materials 
are incorporated retains its tenacity and imperviousness to 
water such coatings will be protective to ironwork, but 
when water is able to make its way to the iron surface it 
seems only too probable that the presence of iron oxide in 
the paint is likely to cause corrosion by acting as the electro- 
negative element in a couple, in the same way as a spot of 
rust on the bright blade of a knife or razor will, if not rubbed 
off, grow over the whole blade. 

The artificial oxide reds are prepared by the calcination 
of copperas (ferrous sulphate), or by the precipitation of 
ferric oxide by means of milk of lime or alkaline solutions 
from waste iron liquors. The shade of those produced by 
ignition varies according to the temperature and time of 
roasting, from a light red to a purple. The shade of colour is 
also regulated by the presence (either added or naturally) 
of more or less lime salts, or barium sulphate. It is re- 
markable how little the shade of these colours seems to 
depend on the amount of iron present, the physical changes 
produced by roasting having apparently far more effect. 

Below we give the composition of iron-oxide colours of 
various shades, some dry, some ground in oil : — 



RED 


OXIDES. 








I. 


II. 


III. 


Oil . . . . . 






12-3 


Water of combination . 


0-4 


0-6 




Ferric oxide . 


90-5 


96-7 


22-6 


Alumina 








Lime salts, etc. 


2-5 


traces 


23-6 


Insoluble siliceous matter 


6-6 


2-7 


6-2 


Barium sulphate . 






36-4 



100-0 100-0 100-0 



INORGANIC PIGMENTS. 143 



PURPLE AND CHOCOLATE. 



« 



•oa,^ 'd'S.? p. 

3fl£ Sp2 Dark Purple Brown. § Chocolate. 

IV. V. VL VII. vni. IX. X. XI. XII. 

Oil 22-6 — — — 14-0 14-6 lO'O — — 

Water of combination . — 0*6 — — — — — — — 

Ferric oxide . . . 57*2 93-6 97*4 85-4 84*1 807 18*4 97*8 90*0 

Alumina . . . — 2-9 — f _ . — — — — 6*8 

Lime salts, etc. ..21— -6 ( — 8*2 . -8 -4 1-0 

Insol. siliceous matter . 18*1 3-0 2*0 7-2 1-9 1-5 6-7 1*8 8-7 

Barium sulphate . . — — — — — — 65*6 — — 



100-0 1000 1000 100-0 100-0 1000 100-0 1000 100-0 

The difference in composition of similarly coloured 
materials, and the similarity in composition of differently 
coloured materials, are well illustrated in these examples. 
Compare I. and II. with III. ; X. with any of the other 
purples ; II. with VI. 

The darker shades of colours, purple and chocolate, are 
obtained by strongly igniting the red oxides, the higher 
the temperature of ignition the deeper and more violet is 
the colour obtained. 

Mars Colours. 

The Mars colours are a series of artificial oxide of iron 
colours prepared by precipitating ferrous sulphate with milk 
of lime, drying the resulting mixed precipitate of ferrous 
hydroxide and calcium sulphate in the air — when the ferrous 
hydroxide becomes oxidised to the ferric compound — and 
roasting or strongly igniting ; according to the temperature, 
a yellow, orange or brown pigment is obtained. These colours, 
like all the ferric oxide colours, are absolutely permanent. 

Terre Verte (Green Verona Earth). 

This natural green pigment is found at Verona, in Italy, 
and at Cyprus. It is extremely permanent, and owes its 



I 



144 CHEMISTRY OF PIGMENTS. 

colour to the presence of ferrous oxide, probably combined 
as a silicate. We give the composition of two samples 
examined by some rather ancient authorities : — 

Berthier or TrinT>i.nfh 
Delesse. Klaproth. 

Verona. Cyprus. 

Silica 61-21 61-5 

Alumina 7 26 — 

Ferrous oxide 20*72 20-6 

Magnesia 6*16 1*5 

Soda 6-21 — 

Potash — - 18-0 

Water 449 80 

Manganese oxide .... trace — 

9604 99-5 

These analyses are not very satisfactory, but both seem 
to indicate that the substance is a ferrous alkaline silicate. 
The presence of soda and magnesia in the Verona sample, 
and of potash with only a small quantity of magnesia in 
that from Cyprus, is of interest. 

The Veronese earth is usually of a purer green than that 
from Cyprus, which is of a verdigris to apple-green colour. 

Prussian Brown. 

This colour, which is not used to any great extent, is 
prepared by the careful ignition of Prussian blue. It consists 
almost entirely of ferric oxide. Prussian blue on ignition 
gives off cyanogen and apparently leaves a residue of metallic 
iron which, being in an extremely fine state of division, readily 
burns, becoming red hot, to a brown oxide of iron. Should 
the temperature become too high the product is too dark. As 
Prussian blue is never pure ferric ferrocyanide but always 
contains alkali-iron cyanide and usually other alkaline salts, 
it is, even when using genuine samples of blue, not always 
easy to ensure regularity of tint in the brown pigment. This 
brown can be diluted to shade by means of the ever-useful 
barytes or other white pigments. 



INORGANIC PIGMENTS. 145 

The analysis of the iron oxide pigments does not present 
very great difficulties. In the case of red and yellow pig- 
ments the following method of procedure should be adopted. 
A suitable amount, say 1 to 2 grams, of the dry pigment is 
weighed in a platinum or porcelain capsule and ignited to a 
dull red heat. In the case of a dry pigment the loss repre- 
sents the amount of moisture and water of hydration with, 
in some cases, traces of organic matter. The residue after 
ignition is scraped into a beaker and treated with concen- 
trated hydrochloric acid, notice being taken whether effer- 
vescence occurs (indicating presence of a carbonate). After 
standing in the water-bath from half to three-quarters of an 
hour the contents of the beaker are examined and, if the 
insoluble residue does not appear reddish, diluted with water, 
allowed to stand for any insoluble matter to deposit, and 
filtered. The residue in the filter is washed, ignited without 
drying, and weighed. It may be silica or clay, or barium 
sulphate with one or both of these. Fusion with alka- 
line carbonates will convert silica into alkaline silicates 
soluble in water, clay into alkaline silicates and aluminates, 
and barium sulphate into barium carbonate and alkaline 
sulphates. It is usually only desirable to determine the 
amount of barium, which, being usually weighed as sulphate 
and occurring in pigments in this form, is returned as such. 

If the residue from the HCl treatment is coloured it 
should be re-treated, after weighing, with acid and re-filtered. 
The filtrate is mixed with the original filtrate and the in- 
soluble matter again weighed. It can then be determined 
whether a further treatment is necessary or not. The whole 
of the filtrate and washings is diluted to 250, 500, or 1,000 c.c, 
according to circumstances, and a convenient aliquot part, say 
^, taken, diluted if necessary, and ammonia, in slight excess, 
added. The liquid is heated to boiling to expel the excess 

of ammonia. The precipitate is washed once or twice by 

10 



146 CHEMISTRY OF PIGMENTS. 

decantation, transferred to the filter and allowed to drain. 
It is then re-transferred to the beaker, re-dissolved in large 
excess of hydrochloric acid, suitably diluted and re-precipitated 
'with ammonia. By this means any co-precipitated lime is 
removed and a precipitate consisting only of ferric oxide and 
alumina (with possible traces of PgO^ and CrgOg) obtained. 
This is weighed. The iron can be determined in another 
portion of the original hquid by titration vdth ^ KgCrgO^ 
after reduction or in the redissolved weighed ammonia pre- 
cipitate. The former is the more expeditious method. The 
filtrate from the ** ammonia precipitate '* contains the lime, 
magnesia, etc. These may be determined or not as desired. 
The hygroscopic moisture should be determined in a separate 
portion in a water oven at lOO*'. 

In the case of pigments ground in oil it is usually suiB&cient 
to determine the total loss on ignition, and not to determine 
the actual percentage of oil, though, of course, for scientific 
purposes it is certainly better to do this. The determination 
can be effected in the manner described under " white lead ". 

The brown pigments present rather more difficulty, as 
many of them contain manganese. The best method, in this 
case, is to, in the original (filtered) hydrochloric acid solution, 
adopt the method of separation based on the behaviour of 
the acetates of iron and alumina on heating. The hydro- 
chloric acid solution is nearly neutralised with ammonia, 
care being taken, however, to leave a slight amount of free 
acid, and then a saturated solution of sodium acetate added 
in sufficiency to be in slight excess. The liquid, which was 
yellow, becomes of a deep red colour, owing to the formation 
of ferric acetate, and smells of acetic acid. This liquid on 
boiling becomes turbid and deposits a flocculent precipitate of 
basic ferric (and aluminic) acetate. The manganese remains 
in solution. The basic ferric acetate (or mixed acetates as 
the case may be) is collected and washed ; in very accurate 



INOEGANIC PIGMENTS. 147 

analyses, Fresenius recommends re-solution and precipitation, 
but this is not usually at all necessary : the precipitate is 
then dried, ignited, and re-dissolved in HCl, precipitated by 
ammonia as hydroxide, collected, weighed, and the amount of 
iron determined by titration, after reduction, with ^^ KgCrgO^. 
By this means the percentages of iron oxide and alumina 
can be determined. In the filtrate from the basic acetates 
manganese can be determined by making alkaline with 
ammonia, with the addition of ammonium chloride, and 
either passing sulphuretted hydrogen or adding ammonium 
sulphide. Manganese is precipitated as sulphide.^ The 
precipitate is collected, washed, and weighed, either as 
sulphide after ignition with sulphur in a current of H2S, or 
re-dissolved in HCl and precipitated by NagCOg as MnCOg, 
which on ignition becomes Mn304. The filtrate from the 
manganese may contain lime, magnesia, etc. Ammonium 
oxalate, in slightly acetic solution, will precipitate the lime, 
which can be weighed as carbonate or oxide, and the filtrate, 
after concentration, can be treated with ammonia and sodium 
or ammonium phosphate to precipitate the magnesia as 
MgNH^PO^, which on careful ignition becomes Mg2P207 ; but 
this is seldom necessary. 

VI.— COBALT COLOURS. 

The metal cobalt enters into the composition of some few 
colours, in each case as the chromogenic constituent. These 
cobalt colours may be considered as of three kinds : (a) pig- 
ments formed of a white basic oxide with cobalt oxide ; (b) 

^ It is desirable that a considerable quantity of ammonium chloride 
should be present in the solution from which manganese sulphide is to be 
precipitated, and that the solution should stand twenty-four hours after the 
addition of ammonium sulphide before filtering. The sulphide should be 
washed with water containing ammonium sulphide, and the funnel not 
allowed to remain empty after each washing runs through, as otherwise 
oxidation may occur, and manganese pass through the filter. 



148 CHEMISTRY OP PIGMENTS. 

silicate of cobalt ; (c) cobalt potassium nitrite. We will con- 
sider these three classes. 



(a) Cobalt Oxide with a Basic Oxide. 

CobaIjT Blue (Cobalt Ultramarine, TMnard's Blue), — Cobalt 
blue is, according to its method of preparation, a mixture of 
either oxide, phosphate or arsenate of cobalt with alumina, 
and is a fine deep blue, somewhat like ultramarine, but with 
a tendency to violet which is more marked in artificial light. 
It is prepared by precipitating a solution of a cobalt salt 
(the nitrate, acetate or chloride) with sodium phosphate or 
arsenate. The gelatinous violet precipitate thus obtained 
is washed well with water and mixed with three to five 
times its volume (or more in the case of 'the arsenate) of 
freshly precipitated and washed alumina. The mixture is 
thoroughly incorporated and dried until brittle and in a suitable 
condition for ignitioa It is then transferred to a clay crucible, 
which is well covered and ignited to a cherry red for about 
half an hour. It is important that no reducing gases should 
be allowed access to the ignited mass, and Eegnault has sug- 
gested the addition of a small quantity of mercuric oxide which 
gives off oxygen on heating, and the mercury volatilising 
leaves no residue to contaminate the product. It is important 
that the cobalt salt and the alumina used should be free from 
all other metals, the oxides of which are coloured, e.g,, iron 
nickel, manganese. 

Another process by which a similar but inferior colour is 
obtained is, the co-precipitation of the oxides of cobalt and 
aluminium from a mixture of the salts, e,g., cobalt nitrate and 
alum, by means of sodium carbonate. The precipitate of 
mixed oxides is washed, dried and ignited as is, in the former 
method, the mixed phosphate or arsenate and alumina. 

Binden recommends that cobalt chloride should be treated 



INORGANIC PIGMENTS. 149 

with ammonia to precipitate the oxide, which, after washing, 
is mixed with alumina and ignited. 

Cobalt blue is permanent, non-poisonous and a fine colour,, 
though, as already stated, somewhat inclined to violet. It 
lacks the brilliance of ultramarine, which as a blue is unsur- 
passed. 

Cobalt Pink. — This pigment is prepared by mixing mag- 
nesium carbonate and a solution of cobaltous nitrate to a 
paste and calcining the mixture, after evaporation to dryness, 
in a covered crucible. 

Cobalt Beown. — A brown pigment is prepared by adding 
ferric oxide to the mixture of alumina and cobalt salt used 
for making the blue, or by igniting ammonia alum with 
cobalt sulphate and ferrous sulphate ; a high temperature is 
requisite for the carrying out of this latter process. 

These cobalt-basic-oxide compounds, from the fact that 
the presence of reducing gases in the crucible damages the 
pigment, and that the addition of mercuric oxide or man- 
ganese dioxide tends to improve the pigment, would appear to 
be cobaltic compounds. 

Another pigment which to some extent belongs to this 
class is 

Coeruleum (CcgZin, Bleu Celeste). 

This pigment, which is lighter in colour than cobalt blue, 
is apparently a stannate of cobalt, mixed with calcium 
sulphate and silica. It is said to be in a state of purity, 

8 (SnOaCoO) + SnOg. 

An analysis given by an unknown authority is as follows : — 

Stannic oxide ' . . 49*66 

Cobaltous oxide 18*66 

Calcium sulphate and silica 81*68 

100-00 

Cobalt Green (Binmanns Green). — When cobalt oxide is 



150 CHEMISTRY OF PIGMENTS. 

ignited with oxide of zinc instead of oxide of aluminium, a 
green colour is obtained; this fact is well known to those 
who are accustomed to blow-pipe analysis. 

This cobalt green is prepared by precipitating from a pure 
cobalt salt in solution (10 per cent.) the phosphate or arsenate, 
and, after washing, mixing the precipitate with zinc oxide, 
and igniting. Sodium carbonate may, less satisfactorily, be 
substituted for sodium phosphate or arsenate, or a mixed 
solution of zinc sulphate and cobalt nitrate may be precipi- 
tated by sodium carbonate. Another method is to mix a 
solution of a cobalt salt with zinc oxide, evaporate to dry- 
ness and ignite. 

Some analyses of this pigment are given by E. Wagner. 
One from the University of Wiirzburg had the following 
composition : — 

Zinc oxide 88040 

Ferric oxide 0*298 

Cobaltous oxide 11-662 

100000 

This was a light green. 

Two samples prepared by himself agreed more with what 
might be expected from the former mode of preparation 
described by us : — 

Zinc oxide 71-93 71*68 

Cobaltous oxide 19-16 18*93 

Phosphoric anhydride .... 8*22 8*29 

Sodium oxide 0*69 — 

99*99 98*90 

The sodium oxide was probably present as an impurity due 
to imperfect washing. 

(b) Cobalt Silicates. 

Smalt (Bleu d'azwr^ Bleu de Saxe — Saxon blite), — Smalt is 
a blue colour prepared in Saxony and in Norway, in the 



INOEGANIC PIGMENTS. 151 

former country usually from smaltine (smaltite), an analysis 
of which by Hofmann is given below : — 

SMALTINE FROM SCHNEEBERG. 

Arsenic 70*37 

Cobalt 18-95 

Nickel 1-79 

Iron 11-71 

Copper 1-89 

Sulphur 0-66 

Bismuth 001 

99-88 

The typical kind is (Co, Fe, Ni) Asg. 

In Norway oobaltite CoAsS (or C0S2 + C0AS2) is the ore 
used. 

Smalt is a silicate of cobalt and potassium, and is pre- 
pared by fusing a crude cobalt oxide with potassium carbonate 
and quartz. The process is conducted in several stages. 

The ore is first carefully selected and all casual impurities 
rejected, and is then placed in charges of about three cwt. in 
a layer five or six inches thick, on the bed of a reverberatory 
furnace or in a muffle, the object being to roast it in a current 
of air. By this means the sulphur and a great part of the 
arsenic is expelled as SOg and AsgOg respectively, the latter 
oxide being collected in condensing chambers. The roasting 
should be continued until only sufficient arsenic is left to 
combine with the less oxidisable naetals, the coBalt being 
converted into oxide. Test portions are taken out from time 
to time until the tint of the glass obtained is satisfactory, 
when the roasting is stopped. 

Pure quartz ignited, then slaked and crushed, is washed 
by levigation from any iron oxide or other impurities. This 
is mixed with pure potassium carbonate, about one part of 
the latter being used for three parts of roasted ore and the 
same quantity of quartz, and some arsenious oxide added to 
oxidise any ferrous oxide present. The exact amount of 



152 CHEMISTRY OF PIGMENTS. 

these ingredients required is ascertained by making small 
tests. 

Very refractory melting pots are used and placed in a 
furnace similar to that of a glass oven. This is raised to a 
very high temperature and in about eight hours the mass fuses. 
It is from time to time stirred to thoroughly mix and to break 
up any crust which may form on the surface of the melt. At 
a white heat the cobalt oxide begins to be attacked by the 
silicate and a blue glass is formed. The mixed arsenides of 
the other metals with some cobalt sink to the bottom of the 
pot and form a brittle metallic-looking speiss. The mass 
is left for some time at a white heat to allow this to settle 
completely and the smalt ladled out into vessels of cold water. 
An easily pulverised glass is thus obtained. The speiss, which 
begins to be scooped up with the smalt as the bottom of 
the vessel is neared, is more fusible and may be poured 
out from under the blue into a niche connected with the 
furnace chimney, thus allowing the fumes of arsenic to 
escape. 

The glass is now crushed, ground fine and levigated. As 
it is a more or less transparent substance the portions of 
medium fineness are more suitable for colouring purposes 
than the very finely ground portions, which must be re- 
smelted. 

The presence of other oxides than those of cobalt and 
potassium is prejudicial to the colour of the product ; baryta 
gives a deep indigo tint, sodium, calcium and magnesium 
produce a reddish shade, iron a blackish green, manganese 
violet, nickel a less intense violet ; copper, zinc, bismuth and 
antimony give dull shades. 

The composition of three samples of smalt examined by 
Ludwig (from Thorpe's Dictionary) is given below : — 



INORGANIC PIGMENTS. 



153 





Norwegian 

deep-coloured 

sample. 


German 

deep 
coloured. 


German 

pale 

coarse. 


Silica 


70-86 


66-20 


72-12 


Potash and soda 


21-41 


16-31 


2004 


Gobaltous oxide 


6-49 


6-75 


1-96 


Alumina . . . , 


0-43 


8-64 


1-80 


Protoxide of iron . 


0-24 


1-36 


1-40 


Arsenious acid 


tvBioe 




0-08 


Water and carbonic acid 


0-67 


0-92 


0-46 




100-00 


100-18 1 


97-86 



(c) Aureolin (Potassio Cobaltic Nitrite). 

This deep lemon-yellow pigment is prepared by adding 
potassium nitrite to a cobaltous solution acidified with acetic 
««cid. Nitrogen is set free and the salt separates as a yellow 
<5rystaUine powder — 

C02 (N02)6 6KNO2 + nHgO. 

It is desirable to use strong solutions, as otherwise relatively 
large crystals are formed and the pigment has little covering 
power. 

Aureolin, sometimes called Indian yellow, is a very per- 
manent yellow, but from the nature of its constituents is 
•expensive and only suitable for artists' use. It works well 
in both oil and water. It is quite a modern colour. 

- VII.—COPPER PIGMENTS. 

Copper Greens. 

The hydrated and some other compounds of copper are, 
«.s is well known, usually of a blue or green colour, and 
some of these have from very early ages been used as green 
•colours. The compounds principally used are the basic 
carbonate, the basic acetate, and the arsenite and aceto- 
arsenite ; the ba,sic chloride was also formerly used under the 



^ This total is given in the Dictionary as 101-18. 



154 CHEMISTBY OF PIGMENTS. 

name of Brunswick green, which name is now applied to- 
Prussian blue green, a chromate. We will consider these 
colours individually. 

Malachite {Basic Carbonate of Copper, Green Verditer, 
Green Bice, Mountain Green — Vert de Montagne, Berggrim). — 
This pigment is the most ancient of all the copper greens ; 
Sir H. Davy in his researches on the pigments found in the 
baths of Titus and Flavia and other ruins at Rome and 
Pompeii found this pigment used for mural decoration. 

Malachite is a mineral found in various localities in 
Europe, Africa^ America and Australia. The following list 
is from Dana : The Urals ; at Chessy in France ; at Schwatz; 
in the Tyrol ; in Cornwall and in Cumberland ; Sandlodge 
Copper Mine in Scotland ; Limerick, Waterford and else-^ 
where in Ireland ; at Grimberg, near Siegen, in Germany ; 
at the copper mines of Nischne Tagilsk ; at Bembe on the 
west coast of Africa ; with the copper ores of Cuba, Chili ^ 
Australia, and in New Jersey, Pennsylvania, Winsconsin and 
California. 

The mineral which is highly valued for ornamental 
purposes is named from fiaXaxv* rnallows, in allusion to its. 
green colour ; and its composition corresponds to CuCOg Ca 
(0H)2. This corresponds to 

CO2 19-9 

CuO 71-9 

H2O 8-2 

1000 

Malachite only requires careful selection of pure pieces — 
free from ochreous matter, and grinding to render it fit for 
use as a pigment. 

Church states that ** Malachite as an oil paint has often 
proved to be permanent, although it may seem to acquire 
a dull, brownish hue, owing to the darkening and yellowing; 



IXORGAXIC PIG^TEXTS. 155 

of the oil ; sometimes, however, it becomes somewhat olive 
in colonr ". 

Various artificial preparations have from time to time 
been proposed in place of this very expensive mineral for 
use as pigments. We give in the next sections a description 
of the preparation of some of these and of similar blue 
substances. 

Bremen Green {Green Verditer). — This colour, which is 
now but httle used except, we beheve, by artists and paper 
stainers, consists chiefly of basic carbonate of copper, mixed 
with alumina and calcium carbonate. According to Bley, 
a fine blue-green colour is obtained by dissolving copper 
sulphate in 10 parts of water, adding a little nitric acid, 
leaving the solution to itself for a week, then filtering, adding 
fresh Hme water, precipitating with filtered solution of pearl 
ash and mixing the washed product with gum water to give 
it lustre (Watt's Dictionary of Chemistry). The object of adding 
nitric acid is to prevent precipitation of copper carbonate by 
the lime salts in the water used for solution, and the pro- 
longed keeping of the solution facilitates the precipitation 
of any insoluble impurities. Another action of nitric acid 
would be to oxidise any ferrous salts present as impurities, 
which means that any precipitate due to iron is yellow ferric 
hydroxide, which is permanent, and not greenish ferrous 
hydroxide, which will become yellow. 

At Bremen and Cassel this pigment is, according to 
Gentele, prepared by grinding 225 lb. of sea salt with 222 lb* 
of crystallised copper sulphate and water to a thick paste. 
* With this, 225 lb. sheet copper, cut into pieces about 1 in. 
square, is mixed in strata in a wooden chest made without 
nails, and digested for three months, with stirring about once 
a week. At the end of this period the undissolved metal is 
removed and the precipitate washed with the minimum 
amount of water. One hundred and eighty pounds of this 



156 CHEMISTRY OF PIGMENTS. 

is thrown into a tub with 12 lb. of hydrochloric acid of 13"* 
Baume, well stirred and left for twenty-four to thirty hours ; 
to 6 volumes of this, 15 volumes of sodium hydroxide (19° 
Baum6) and afterwards 6 volumes of water are added. The 
precipitate is washed, filtered, exposed to the air, and dried. 

Another method, described by Habich, is to treat copper 
sheathing with about equal parts of potassium sulphate and 
sodium chloride, forming a paste of the mixture and stirring 
for some months, or to treat 100 parts of copper with 60 parts 
of salt and 30 parts of sulphuric acid diluted with three times 
its volume of water, exposing for some time to the fresh air, 
and in either case to treat the magma (100 kilos) with copper 
sulphate (7 kilos) and concentrated soda solution (40 kilos) ; 
then stir vigorously and pour into 150 kilos of sodium hy- 
droxide (20'' Baum6) wash, pass through hair sieves and 
dry at a temperature not above 78° F. 

In these processes, which appear to be unnecessarily com- 
plicated, it would seem that under the influence of air and 
hydrochloric acid, or air and alkaline chloride, copper becomes 
converted into basic chloride or copper oxy-chloride, which is 
then converted into an hydroxide which may or may not be 
allowed to carbonate. 

In the process described by Gentele it is conceivable that 
a double decomposition occurs thus : — 

CUSO4 + 2 NaCl = CuClg + Na2S04, 

cupric chloride acting on copper forms cuprous chloride — 

CuCLj + Cu = CU2OI2. 

This, on oxidation, may become an oxy-chloride — 

CU2CI2 + O = CuClj CuO. 

The object of adding hydrochloric acid to this is difficult to see, 
and the addition of caustic soda should result in the formation 
of cupric hydroxide and not carbonate. Unless it is the case 



INORGANIC PIGMENTS. 157 

that a certain amount of oxy-chloride is left in the colour it is 
most difficult to understand why such complicated processes 
are used apparently only to produce cupric hydroxide. 

Scheele's Green {Cupric Arsenite, Swedish Green, Mittis 
Green, Scheele's Grim, Vienna Green, Veronese Green). — This 
pigment, discovered by Scheele in 1778 is an arsenite of 
copper containing an excess of copper oxide, prepared by 
precipitation. 8cheele*s original process was to dissolve 
1 part of arsenious anhydride and 2 parts of potassium 
carbonate by boiling in 35 parts of water, filtering if 
necessary, and adding until no further precipitation occurs 
to a solution of 2 parts of copper sulphate in water. The 
precipitate was collected, washed and dried at a gentle heat 
(it will not bear ignition). Church recommends that solu- 
tions of arsenious acid and copper sulphate should be mixed 
and potassium carbonate added until the maximum intensity 
of colour is obtained. Various other methods have been 
adopted, but the pigment is not much used now, having 
become very much discredited owing to its poisonous nature 
and inferiority to other copper-arsenic compounds. It is a 
pale but not very bright green and can be readily distin- 
guished from malachite on the one hand and emerald green 
on the other by giving a reaction with Marsh's test, a sub- 
limate of arsenious acid on heating, and not effervescing 
with dilute mineral acids (differences from malachite), and by 
not giving off acetic acid vapours on heating with strong 
sulphuric acid (difference from emerald green). 

Emerald Green (Cupric Aceto- Arsenite, Schweinfurt Green, 
Paris Green). — This pigment, which has now" almost super- 
seded Scheele's green, is a most brilliant colour. It is a 
mixture or compound of arsenate and acetate of copper 
supposed to correspond to 

3 CuO AsjOj Cu(C2H302)2. 



158 CHEMISTRY OF PIGMENTS. 

Various methods of preparation are employed, of which the 
following are of interest. 

Five parts of verdigris (basic acetate of copper) made into 
a thin paste with water are added to a boiling solution of 
more than 4 parts of arsenic trioxide in 50 parts of water, the 
solution being kept boiling during the addition, and acetic 
acid being added if a yellowish-green precipitate separates. 
On further boiling for a few minutes the precipitate becomes 
crystalline and of the characteristic bright green colour. 

Boiling concentrated solutions of arsenious oxide and 
copper acetate are mixed in such proportions that equal 
weights of the two substances are present, when a bulky 
olive-green precipitate falls — the liquid is diluted with an 
equal volume of water and the mixture placed in a flask 
which is filled to the neck to prevent any pellicle which 
forms on the surface from falling and starting premature 
crystallisation. 

The colour thus prepared separates out in the course of 
two or three days and owes, it is supposed, much of its beauty 
to the gradual nature of its formation. 

We give the composition of some samples of emerald 
green examined by us : — 

Deep. Light. 

Moisture — 1*6 

Arsenious oxide .... 56*6 52*7 

Cupric oxide 35*0 31*5 

Acetic anhydride, etc . . . 8*4 14*2 
Insoluble in acid .... — — 





1-1 


49-4 


46-8 


28-2 


26-2 


14-6 


13-1 


7-8 


12-8 



100-0 100-0 100-0 1000 

These samples were most brilliant colours; the light 
greens were *' lowered" with barium sulphate. 

The ratio of arsenious oxide to cupric oxide in each of 
these four samples is approximately 2 molecules to 3 mole- 
cules. The actual figures work out 

1:1-55, 1:1-50, 1:1-44, 1:1*40. 



INOBGANIC PIGMENTS. 159 

The ratio calculated from the formula ascribed to the pure 
compound is SASgOg : 4CuO, and the percentage composition 

AS2O3 58-7 

CuO 31-2 

(C2H30)20 101 



1000 

The excess of copper found is probably due to the presence 
of verdigris or other basic-copper compounds. 

Emerald green is dissolved by acids without effervescence 
to a blue or green solution ; on warming the solution acetic 
acid is evolved. Marsh's and Eeinsch's tests indicate the 
presence of arsenic. On ignition it is blackened with evolu- 
tion of acetous vapours and formation of a white sublimate 
of arsenious anhydride. 

The analysis of the copper-arsenic colours presents no 
great difficulty. A portion, not more than 1 gram, is treated 
with hydrochloric acid and nitric acid or potassium chlorate 
added to oxidise the arsenious to arsenic acid, the liquid 
diluted, and, if necessary, filtered from any insoluble matter, 
which should be weighed. The filtrate, in the known absence 
of lead or other heavy metals, is made strongly alkaline 
with ammonia and excess of magnesium mixture added. 
Magnesium ammonium arsenate forms, and after some hours 
standing, with frequent stirring, precipitation is complete. 
The precipitate is filtered off and washed, until free from 
dissolved matter, with dilute ammonia. The magnesium 
ammonium arsenate may be weighed as such after very long 
drying at 105° C, or, better, is slowly ignited at a gradually 
increasing temperature until all NH3 is expelled, and the 
residual magnesium pyroarsenate MggAsgO^ weighed. The 
filtrate from the arsenic contains all the copper as blue 
ammonio-cupric salt. This is concentrated and acidulated 
with hydrochloric or sulphuric acid, transferred to a weighed 
platinum dish and zinc added. The copper is precipitated 



160 CHEMISTRY OF PIGMENTS. 

on the platinum and when all the zinc is dissolved, and the 
Hquid carefully poured off, the spongy copper is pressed to- 
gether and washed repeatedly with hot water, then with alcohol,, 
and lastly with ether. This should be done quickly and the 
dish dried in the water oven. The increase in weight gives 
the weight of copper present in the amount of green taken. 
The supernatant liquid from this operation should be tested 
with a fresh piece of zinc and a few drops of acid, for any 
copper not precipitated. If carefully carried out this process 
is very accurate ; excess of zinc is necessary to precipitate all 
the copper and excess of acid to dissolve all the zinc. A test 
with zinc and acid alone should show no residue insoluble in 
acid ; if this is found the zinc is unsuitable for the purpose. 

If lead is present it can be removed by precipitation with 
a large excess of diluted sulphuric acid. The. lead sulphate 
should be washed twice with dilute sulphuric acid to remove 
arsenid and copper, and then with alcohol to remove sul- 
phuric acid. Any precipitate with ammonia should be filtered 
off and examined before precipitating the arsenate. Lead 
chromate, which might be used to lighten the pigment, 
would, after solution in HCl give a precipitate of chromium 
arsenate under these conditions. 

Verdigris {Vert de Gris, Grunspan), — Under the name 
verdigris several of the acetates of copper are included ; 
those which are of importance as pigments are hltie verdi- 
gris — dibasic cupric acetate, and green verdigris — a mixture 
of di- and tri-basic acetates, or a sesqui-acetate. Blue verdi- 
gris is prepared at Montpellier and other parts of France by 
exposing copper plates to the air in contact with fermenting 
wine lees or marc. The acetous fermentation sets up, and 
verdigris forms. The plates are, after about three weeks' 
action, taken out, placed in an upright position to dry^ 
dipped in water about once a week for six or eight weeks, 
and the verdigris, which swells up, is scraped off. The plates 



INORGANIC PIGMENTS. 



161 



are then again treated with wine lees and re-treated until 
entirely corroded. When the plates are new action is facili- 
tated by brushing them with a solution of normal acetate of 
copper. 

Blue verdigris is also formed by exposing copper plates to 
damp air in contact with a paste of the normal acetate and 
water. 

It is obvious that, whatever process is used, old corrugated 
copper plates will give a better yield by reason of the greater 
surface they present than new bright plates. 

Verdigris forms silky blue needles and scales which grind 
to a beautiful blue powder. It is CuO, Cu(C2H302)2 + 6H20. 
On heating to 60** C. the water is given up and a green mixture 
of a more basic salt and the neutral acetate is formed — 

20uOCu(C2H302)2 = Cu(C2H302)2 + Cu(C2H503)2 2CuO. 

Repeated exhaustion with water causes the formation of 
normal cupric acetate with two other basic acetates thus : 

■ 

5(C2H302)2Cu, CuO = 2(C2H302)2Cu, 2CuO + (02H.02)4Cu2, CuO + (C^Hfi^fiu. 

The composition of samples examined by Berzelius and 
Phillips is given in Watts' Dictionary of Chemistry. 

PhUUps. 



Theoretical 




French. 


EDff 

Crystallised. 


lish ^ 


for (C2H302)2 CuCuO, 6H2O. 


Berzelius. 




Compressed 


CuO . . . 43-24 


43-34 


43-5 


43-25 


44-26 


(C2H30)20. . 27-57 


27-46 


29-3 


28-30 


29-62 


6H2O . . 29-19 


29-21 


25-2 


28-45 


26-61 


Impurities . — 




20 




0-62 


100-00 . 


10000 


100-0 


10000 


10000 



Green verdigris, which according to Berzelius is the salt 

2(C2H302)2Cu, CuO + 6H2O with small quantities of bi- and 

tri-basic acetates and sometimes cuprous acetate, is prepared 

at Grenoble by sprinkling copper plates with vinegar and 

keeping in a warm damp room, and in Sweden by packing 

copper plates and flannel alternately and moistening with 

11 



■^ 






162 CHEMISTRY OF PIGMENTS. 

vinegar. The greenest kind, Berzelius stated, contains 49*9 
per cent. CuO and 13*5 per cent, water and impurities, while 
the pure sesqui-acetate contains 43*5 per cent. CuO. 

Brunswick Green. 

The pigment formerly known by this name was oxy- 
chloride of copper CU4CI2O3, 4H20 = CuCl2 3CuO, 4H2O, pre- 
pared by moistening copper turnings with hydrochloric acid 
or a solution of ammonium chloride and leaving them in 
contact with the air. The oxy-chloride forms on the surface, 
and is washed off with water and dried at a gentle heat. 

The much used pigment now known by this name is 
of very different composition, namely, Prussian blue and 
chrome yellow diluted with barium sulphate. 

A preparation of copper oxy-chloride from copper turnings 
and ammonium chloride gave after drying in the air and then 
over H2SO4 — 

H2O lost at 100° . 1-4 

H2O lost at 175-86° . . . . . . . 15*7 

CuOla 23-0 

CuO 60-4 

100-6 

It was a blue-green which became greener on drying at 
100** and darkened at higher temperatures. It is more basic 
than required by the formula CU4CI2O3, 4H2O — 

4H2O 16-2 

CuCla 30-3 

3CuO 63-5 

1000 

Our preparation agrees fairly closely with 2CUCI2 9CuO, IOH2O. 
It seemed to be a very poor pigment of very little colour- 
ing power when ground in oil. 



INORGANIC PIGMENTS. 163 

Non-Arsenical Green. 

A green brought out in Germany to supersede emerald 
green consisted mainly of malachite brightened by lead 
chromate. It is said to be obtained by mixing copper blue 
(basic carbonate) with chrome yellow, chalk and ferric oxide. 
We give an analysis by C. Struse : — 

Lead chromate 13*65 

Malachite 80*24 

Ferric oxide 0*77 

Calcium carbonate 2*65 

Water 2-68 

99-89 

It never, we beUeve, came much into use and in no way 
equals the brilliance of copper aceto-arsenite. 

Copper Blues. 

Mountain Blue {Blvs Ashes, Lime Bltis, Copper Bltce). — 
The name mountain blue is given to the mineral azurite, 
a native carbonate of copper, and also to a blue prepared 
by precipitating copper hydroxide with lime cream. When 
cupric sulphate is treated with calcium hydroxide, 

CUSO4 + Ca(0H)2 = Cu(0H)2 + CaS04, 

the pigment contains copper hydroxide with precipitated 
calcium sulphate, and when, as is sometimes done, potassium 
carbonate is mixed with the lime, calcium carbonate also 
remains in the washed blue. This blue is, we beUeve, used 
to some extent for distemper work, but we have never seen 
a commercial sample. 

This substance in the moist condition has, under the name 
**bouille Bordelaise,'' been used with success as a spray for 
checking the ravages of the potato disease, phytophthyra 
infestans. It is a very pure sky-coloured blue. 

By precipitating cupric nitrate with chalk and adding 



164 



CHEMISTRY OF PIGMENTS. 



to the precipitate 8 to 10 per cent, freshly burnt Hme, a blue of 
this kind is obtained. Without the lime a green pigment 
results. 

A peculiar blue described by Halich is obtained by dis- 
solving cupric oxide in nitric acid and treating with KgCOg 
until almost but not quite all the copper is precipitated ; then 
washing the precipitate with water, and introducing it into 
a solution of copper nitrate. An insoluble heavy green basic 
nitrate is formed, which, digested with a solution of zinc 
oxide in potash, forms a dark blue of great body but little 
weight, which contains both zinc and copper, and is apparently 
a double oxide with basic copper nitrate. 



VIII.—ULTRAMARINE. 

Keal ultramarine is obtained from a somewhat rare 
mineral, lapis lazuli, a variety of Haiiynite thus described by 
Dana : " Not a homogeneous mineral, according to Fischer 
and Vogelsang. The latter calls it a mixture of granular 
calcite, ekebergite, and an isometric ultramarine mineral, 
generally blue or violet. Much used as an ornamental 
stone.** It is, as the two following analyses will show, of 
very variable composition : — 



Qmelin. 




Fuchs. 




Silica 


. 49-0 


Phosphoric acid 


. 41-81 


Alumina . 


. 11-0 


Alumina 


. 35-73 


Lime 


. 16-0 


Magnesia 


. 9-34 


Soda and potash 


. 8-0 


Silica 


. 2-10 


Oxide of iron . 


. 4-0 


Protoxide of iron . 


. 2-64 


Magnesia 


. 2-0 


Water . 


. 606 


Sulphuric acid . 


. 2-0 




97-68 



92-0 



These analyses are rather ancient, and though by men 
eminent in their day, seem very inconclusive. Speaking 
roughly it would appear to be an aluminium-sodium silicate 
containing sulphur in some form. It is of a blue colour 



INOBGANIC PIGMENTS. 165 

varying according to circumstances. Lapis lazuli is the 
" sapphire '* of the ancients and is evidently the material 
referred to in Bevelation xxi. 19. It is occasionally found with 
gold-like fragments of iron pyrites interspersed through its 
substance. To prepare the pigment, the mineral is broken 
into small pieces, freed as much as possible from mechanic- 
ally adhering impurities, heated in a crucible and thrown 
into cold water or very weak vinegar. It is then washed by 
decantation, dried, ground and then purified by elutriation, 
by which process various grades of colour, from the finest 
blue to grey ultramarine ash, are obtained. Ultramarine is 
the purest and most beautiful blue pigment known and most 
closely approximates in tint to the pure blue of the sky. 
Real ultramarine, on account of the rarity of lapis lazuli and 
the troublesome process of preparation, is a most expensive 
colour. 

In the year 1828 Guimet, stimulated by a prize of 6,000 
francs offered by the Societe d'Encouragement de France, 
discovered a method of preparing artificially a blue similar in 
properties and composition to natural ultramarine. Alkali 
makers had previously noticed spots of ultramarine on their 
furnaces, and efforts had been made to determine the con- 
ditions of formation of this pigment. Gmelin, whose analysis 
has been quoted, also discovered at about the same time a 
method of formation. 

Blue ultramarine was formerly solely made by the ** in- 
direct process," in which sulphate of soda, kaolin and char- 
coal are ground together and burnt in crucibles in a suitable 
oven for six to nine hours. The mass is then turned out and 
is of a dull green colour. It is then crushed and heated on 
a roasting furnace with powdered sulphur, the mass being 
continually stirred until the sulphur has burnt off and a 
bright blue mass is left. Though the materials are cheap 
the process is troublesome and the result is somewhat uncer- 



166 CHEMISTBY OF PIGMENTS. 

tain. The product obtained is poor in silica, and though of 
pure tint is of very weak colour. 

The direct process, which is now adopted very largely, 
requires great care both as to details and in the selection 
of materials. The mixture consists of about 100 parts of 
china clay, 90 of soda, 110 of sulphur, 20 of charcoal and a 
variable amount of infusorial earth, the amount of this latter 
material depending on the quality of ultramarine required. 
The china clay must be very pure and free from sand and 
other rough matters. The soda is the best soda ash, known 
as carbonated ash, and should test 58 per cent, (total alkali as 
NaaO). The raw materials are intimately mixed and finely 
ground. The ignition is conducted in ovens of either of two 
patterns, ''crucible" or **mass" ovens, of which the latter 
is the newer, and, in the opinion of some, the better form. 
The names explain themselves sufficiently; in the former 
pattern the mixture is filled into crucibles twelve to sixteen 
inches high, the lids being luted on and rows of these 
crucibles piled into the furnace, the heat of which is gradu- 
ally raised to a bright red which is maintained for some 
hours, the time varying with the size of the crucibles and 
the nature of the materials used. Air is as far as possible 
excluded at the close of the operation, and the mass allowed 
to slowly cool. The crucibles are taken out and opened and 
the ultramarine carefully turned out and pieces of overburnt 
material chipped away fr6m the beautiful blue colouring 
matter. The **mass " ovens are arranged with a permanent 
floor and back or bridge ; the mixture is put on the floor and 
banked up until level with the bridge, and is then covered 
with thin tiles luted together with a mixture of sand and 
clay. A hole is left in front for observing the courses of the 
operation and another smaller one for removing samples of 
the burning from time to time. Both these can be closed 
with loose bricks or clay plugs. The temperature is slowly 



INOBGANIC PIGMENTS. 167 

raised to a bright red, when sulphurous flames are seen to 
rise from any cracks or faults in the luting ; these at first 
increase, and as the reaction becomes complete disappear. 
The temperature is maintained at its highest point for twelve 
to eighteen hours or until, in the opinion of the operator, all 
action has ceased. The sample, if properly burnt, is of a 
greenish blue and evolves sulphur dioxide in the air without 
actually burning, and spread on a tile soon cools and be- 
comes a slightly greenish blue. The colours assumed by the 
mixture while burning are successively a yellowish grey 
(initial) brown, green, blue ; the brown colour is unstable and 
in the air, and the material burns to a greenish blue. The 
green is also unstable. If the sample is satisfactory the oven 
is luted up and the mass allowed to cool. This takes a week 
or ten days ; on opening, the mass is a deep blue, the lower 
portions, having been more or less heated, being less brilliant 
than the upper layers. The loss in weight is usually about 
one third, and some considerable shrinkage takes place. The 
mass is washed with hot water in vats with perforated false 
bottoms and coarse filter surfaces to remove sodium sulphate 
and other soluble salts, and is ground between upright stones, 
settled first to remove dirt and unground matter, and then 
the finer matter fractionally settled out, the latter portions 
which settle more slowly being the finer colours. The 
liquid, which still contains colouring matter, is precipitated 
with lime, which, by coagulating the particles, renders their 
removal by filtration more easy. The mixing of the various 
shades so as to ensure uniformity of product is a matter of 
considerable importance as, of course, this considerably 
affects the reputation of the manufacturer. 

Most of the details given above are taken from the article 
by G. W. Bawlings in Thorpe's Dictionary of Applied Chemistry. 

We give the results of analysis of some samples examined 
by us and some given in the article mentioned above : — 



168 



OHEMISTBT OF PIGMENTS. 





German. 


English. 


Oennan, 
violet. 


Parry and Ckwte. 


Moisture 




' > 






— 


0-7 


SiOa . 


. 38-90 


39-61 


42-70 


41-30 


42-26 


41-7 


42-4 


AI2O3. 


. 29-50 


23-95 


24-60 


24-30 


26-79 


25-2 


24-0 


NagO. 


. 21-02 


19-15 


19-95 


17-40 


19-49 


18-8 


18-7 


S 


. 10-84 


13-10 


13-04 


14-80 


12-01 


14-2 
99-9 


15-4 




100-26 


101-66 


100-19 


101-80 


100-55 


101-2 



Comparative analyses of three varieties of ultramarine 
by E. DoUfus and F. Goppelsroder (Bull, de Mulhouse, 1875, 
May; Dingl, pol. /., ccxx., 337, 431) are given below. These 
are of a more ambitious nature than the others quoted by 



us : — 



Silicon « 
Aluminium . 
Sodium as NagO 
Potassium 
Sulphur as SO3 
Sulphur as SO^ 
Sulphur as SgOj 
Sulphur as Na^S 
Free sulphur 
Sodium as Na^ 
Oxygen . 



Oreen. 


Blue. 


Violet. 


17-963 


19-160 


20-440 


17-702 


13-925 


12-735 


10-487 


10-088 


11-110 


0-420 


— 




0-292 


0-600 


0-877 


0-213 


0-441 


0-834 


— 


0-469 


2-536 


3-718 


3057 


1-165 


3-491 


. 8-977 


6-964 


5-345 


4-395 


1-676 


40-363 


38-984 


41-748 


99-994 


99-996 


100085 



These would seem to show that the percentage of silicon 
increases and that of aluminium decreases from the green to 
the violet substance. The analyses, calculated as they are to 
three places of decimals, add up to 100 remarkably closely. 

The structure of ultramarine is crystalline, its form being 
apparently single refracting crystals of the regular system. 
This fact was first observed by B. Hofibnann, and the above 
conclusion as to the structure arrived at by H. Vogelsang. 

The true constitution of ultramarine is still a matter of 
great doubt, though its composition and behaviour to reagents 
have been the subject of investigation on the part of many 
chemists. It is, to say the least, startUng that a compound 



INORGANIC PIGMENTS. 169 

containing only the elements silicon, aluminium, sodium, 
sulphur and oxygen, none of which are recognised as possess- 
ing chromophoric properties, should have so intense a colour. 
The method of production, being of a somewhat violent nature, 
serves only to a very slight extent to indicate the nature of 
the pigment. That it is some sort of double silicate con- 
taining sulphur is evident ; but the internal structure of the 
blue molecule is, so far, merely a matter for surmise. 

The action of reagents tends to throw more light on the 
probable constitution of this pigment. Mineral acids, both 
strong and dilute, attack ultramarine blue, discharging the 
colour and causing an evolution of hydrogen sulphide with 
hberation of sulphur. This seems to point to the existence 
of a polysulphide. Solutions of alkalies do not attack blue 
or green ultramarine but the violet becomes blue. A solution 
of alum slowly decolourises blue ultramarine. Heumann dis- 
covered this ; when blue ultramarine is heated to 120°C. in 
a sealed tube with a solution of silver nitrate for fifteen 
hours a dark yellow amorphous body having the following 
composition is formed : — 

Ag 47-97 

Na 1-07 

Al 9-1 

Si 10-09 

S . . . 4-76 

and H (? HgO) 0-61 

Insoluble siliceous matter (clay) 0*81 

74-40 

It is to be presumed that the difference between 74*4 and 
100*0 is oxygen, which is not mentioned in this analysis. 

It will be seen that in this compound nearly all the sodium 
has been replaced by silver ; it is probable that all is replace- 
«.ble. This compound, silver ultramarine, forms the starting 
point for organic derivatives as ethyl, benzoyl and amyl 
ultramarines ; the existence of these substances, though of 



170 CHEMISTRY OF PIGMENTS. 

interest, can scarcely be said to throw much light on the 
constitution of the parent substance. In addition to these 
organic ultramarines, potassium (blue), lithium (blue), barium 
(yellowish-brown), zinc (violet) and manganese (grey) ultra- 
marines may be formed. In all these cases the silver com- 
pound is acted upon with the iodide or chloride of the radical 
or metal to be substituted. The sulphur of ultramarine may 
be replaced by selenium or tellurium. 

When a mixture of chlorine and steam is passed over ultra- 
marine blue or green heated to 160° to 180° a violet-coloured 
substance ffom which sodium chloride may be extracted is. 
produced. The same substance is produced by the action 
of hydrochloric acid gas and air at 160° to 230° C. This sub-^ 
stance, ultramarine violet, contains the whole of the sulphur 
of the original blue, but the sodium (partly removed as chloride) 
is considerably reduced in amount. The long-continued action 
of hydrochloric acid and air causes the violet substance to 
become rose red, or the red colour may be prepared by passing 
the vapours of nitric acid over the violet at 130° to 160° or by 
the vapours of hydrochloric acid at 128° to 132°. 

The considerable variation in composition of ultramarines, 
of similar colour, and on the other hand the similarity in 
composition of pigments of differing shades, seem to point 
to the conclusion that ultramarine is not a simple substance^ 
either being a mixture of blues of allied composition or of 
a coloured with a colourless substance. 

Notwithstanding the difficulties of the case various workers- 
have from time to time proposed formulae for expressing the 
constitution, or, at any rate, the empirical formulae of 
ultramarine substances. 

E. Hoffmann (Ann., cxciv., 1-22) considers that the pale 
blue kind, poor in silica, has the formula 4(Na2Al2Si208> 
+ NagS^, and that rich in silica and of a deep reddish tint 
is 2(Na2Al2Si30jo) + Na2S4. These, he supposed, are formed 



INOEGANIC PIGMENTS. 171 

by the abstraction of sodium from a white compound, 
thus : — 

White. Blue. 

Blue, poor in silica dlNagAlaSijOg + NagS) - 6Na = ilNaaALjSigOg) + NagS^, 
Blue, rich in silica 2(Na2Al^Si30io + 2 NagS) - 6 Na = 2(Na2Al2Si30io) + NagS^, 

the effect of this being to form polysulphides to which the 
colour is probably in some way attributable. The latter white 
ultramarine has not been discovered. 

Griinzweig found that yellow ultramarine, rich in silica, 
could be made from the blue to which the formula 2(Na2Al2 
SigOio + NagS) is attributed, by the abstraction of sulphur and 
the addition of oxygen, thus 2(Na2AL2Si30io) + Na2S304 is 
formed, the yellow thus appears to be an oxidation product 
of the blue. 

Ungor considered that ultramarine contained nitrogen and 
was Al2Si0203N2. 

Endemann believes in the existence of a '* colour nucleus,'* 
which in the case of white ultramarine is AlNa^OgSg. 

Bottinger (Ann., clxxxii., 306) holds that ultramarine may 
be regarded as the last term of a series of molecular compounds 
of an aluminium silicate with a sodium thio-silicate — a silicate 
in which more or less oxygen is replaced by sulphur. 

Fiirstenau {DingL poL J"., ccxix., 269) finds that only the 
sihcates 4AI2O3, QSiOg and AlgOg, 3Si02 are suitable ; these 
treated with Na2S2 or Na2S5 give the following pigments : — 

(a) 4AI2O5, QSiOg with NsLgSg, pure clear blue of but little colouring 

power. 

(b) 4AI2O3, 9SiOa „ NagSg, pure dark blue with great covering power. 

(c) ALjOg, SSiOa „ NagSj, reddish, dingy-coloured product. 

(d) AlgOg, SSiOg „ NagSj, dark violet blue colour with great tinctorial 

power. 

The former two products are free from alum, but the latter 
two both contain this substance. 

Considering the difficulties attending all investigations 
into the constitution of inorganic compounds, it is not surpris- 



172 CHEMISTRY OF PIGMENTS. 

ing that diversity of opinion should exist as to the true nature 
of ultramarine ; we have endeavoured to indicate the views 
of some workers on the subject, but cannot profess to have 
any preference for the views of any one individual. There 
is certainly an abundant field for work in this direction. 

The method of analysis adopted by- us was to treat a 
portion of about 1 gram in a platinum or porcelain dish with 
hydrochloric acid, carefully covering and, when effervescence 
had ceased, washing back any splashes into the main liquid. 
This was evaporated to dryness in the water bath, moistened 
with hydrochloric acid and again taken to dryness. The dry 
mass was moistened with hydrochloric acid, taken up with 
water and the soluble part filtered from the residue of insolu- 
ble matter and sulphur. This insoluble matter was ignited 
and weighed, afterwards being examined to ascertain whether 
pure silica or not. The alumina is precipitated by addition 
of a slight excess of ammonia, collected, and weighed in the 
usual way. The ignited alumina should be quite white, any 
colour indicating the presence of impurity. The filtrate from 
the alumina contains the alkali (as chloride). This may be 
determined, after addition of sulphuric acid in excess and 
evaporation to dryness in a platinum vessel, by cautiously 
igniting at a very low temperature just sufficient to drive off 
the ammonium salts and sulphuric acid ; the sodium is thus 
obtained as neutral sulphate Na2S04. It is better to weigh 
as sulphate than as chloride, as the latter is volatile at a 
relatively low temperature and loss is likely to occur. 

For the determination of sulphur it is sufficient to evapo- 
rate to dryness with concentrated fuming nitric acid or aqua 
regia, which oxidises sulphur to sulphuric acid. This can be 
determined in the filtered diluted liquid in the usual manner. 

Various methods of examination as to quality have been 
described by different workers. Some of the more reason- 
able of these are described below. 



INOEGANIC PIGMENTS. 173 

Guimet, the discoverer of artificial ultramarine, compared 
blues as to colouring power by weighing out 0*1 gram of 
a standard sample and mixing it with 0*6 gram of pure 
powdered chalk by means of a thin spatula, and diluting a 
similar quantity of the sample to be examined with weighed 
increments of the same chalk until equal tints were obtained. 
Then if the sample under examination requires '7 gram 
(7 times its own weight) to produce the standard tint, the 
colour value standard : sample = 6:7, that is, the sample is 
J better than the standard. 

Another rather remarkable method of examination is to 
ignite at a temperature of about 400° C. in a current of hydro- 
gen. The best samples of the artificial blue become a greyish 
green in about half an hour, the worst in a few minutes. 
Lapis lazuli heated for as long as two hours retains its colour 
in the presence of hydrogen. 

Biichner adopts an alum test ; 0*06 gram ultramarine 
is stirred up with a cold saturated solution of alum and the 
time required for decolorisation, whether minutes, hours or 
days, noted. The longer the blue resists the action of alum 
the better it is likely to be. 

The fineness of grinding and the glazing power of the 
blue put on paper with size are matters of importance more 
particularly to the paper maker. 

IX.— CARBON PIGMENTS. 

Carbon forms the base of most of the black pigments used 
in the arts. In most of these it is employed in some amor- 
phous form, but for the protection of metal- work and as a 
grey paint the mineral graphite finely powdered is used, ground 
in oil. Graphite (plumbago, black lead) is almost pure carbon ; 
its value as a protective coating for iron-work has been 
considered in chapter ii. (p. 47). It has the advantage oi 



174 CHEMISTBY OF PIGMENTS. 

being an absolutely inert substance and can only act as a 
body or rather, perhaps, a skeleton for the boiled oil varnish 
which forms when the paint dries. When the paint becomes 
waterlogged the fact of graphite being strongly electro-negative 
to iron is hardly in its favour. 

The various carbon paints have no great *' drying" pro- 
perties in oil, and require the use of ** boiled " oil or of suitable 
siccative materials. 

Ivory Black (Bone Black), — By the ignition of ivory 
(waste pieces, turning dust, etc.) or bone in a covered vessel 
a good black pigment is obtained. The organic matter (ossein 
and traces of fat) is charred to carbon, and a mixture of this 
with phosphate and carbonate of lime left behind as either 
ivory or bone black. The former, though much of the black 
sold for ordinary purposes is called ivory black, is probably 
only used by artists' colourmen, if, indeed, by them, and the 
cheaper bone black sold for decorators* work. 

We give the composition of average bones and of samples 
of so-cajled ivory black : — 



Bones. Ivory Black. 

Moisture .... 6*91 3-44 1-2 01128-84 

Organic matter (or carbon) . 39*31 2003 13-0 12*82 

Phosphate of lime . . 46*60) 70.47 04.0 49*10 



} 



Carbonate of lime, etc. . 5*78 J 3*24 

Sand 1*40 3*06 1*0 600 

10000 100*00 1000 100*00 

Nitrogen . . . . 4*35 

Ivory black is sometimes moulded into little conical masses 
— probably a little gum is used to give some coherence — and 
sold as soap black ; we give the composition of a sample 
examined by us : — 

Moisture . 3*29 

Loss on ignition (black) 23*41 

Phosphate of lime, etc 70*71 

Insoluble siliceous matter 2*59 

100*00 



. INORGANIC PIGMENTS. 176 

The peculiar manner in which the inorganic matter is 
incorporated with the black in this dye, though diminishing 
its pigmentary power, gives it a beautiful Boftness in working 
which renders it a valuable colour. 

Lamp BlacE (Soot Black, Vegetable Black). — When organic 
matters rich in carbon are burnt a great deal of unbumt 
carbon escapes as " smoke " and condenses, or rather settles 



out as "soot" on the cooler parts of the chimney or other 
draught arrangement. To obtain such black in quantity resin 
or tallow is burnt in a confined atmosphere and the carbon 
liberated collected on the walls of a large chamber, which 
are hung with canvas ; a cone saspeuded in this chamber, 
on lowering, acts as a scraper and detaches the black which 
falls on to the floor. The accompanying illustration represents 



176 CHEMISTRY OF PIGMENTS. 

the manufacture of this pigment, the resin or tallow is burnt 
in the iron pot A, heated by the furnace B. The soot is con- 
densed in C and scraped off by the cone D. 

Bistre. 

This is a brownish-b^ack pigment produced by extracting 
with boiling water soot produced at a very low temperature, 
and consequently containing a considerable amount of em- 
pyreumatic matter. The residue, when this has been 
extracted, is levigated and dried. It forms a warm brownish 
black. It is said to be principally produced from beechwood 
smoke or soot. 

X.— VARIOUS UNCLASSIFIED PIGMENTS 

(Naples Yellow). 

Under the name of Naples yellow various pale yellow 
pigments are sold. The original Naples yellow (giallolini) 
appears to have been the secret preparation of a Neapolitan 
colour maker. Fongeroux de Bonduroy, who made some 
investigations at Naples, where it was by some believed to- 
be obtained from some volcanic product from the adjacent 
mountain Vesuvius, gives the following method of preparation : 
A mixture of 24 parts of white lead, 4 parts of *' diaphoretic 
antimony '' (potassium metantimoniate), 1 part of ammonium 
chloride and 1 part of alum are fused in an earthen crucible 
at a red heat for three hours and the melt broken up on 
cooling, ground and washed. 

Thenard states that this pigment is said to be obtained 
by the *' calcination at the proper temperature of a mixture 
of litharge, hydrochlorate of ammonia (sal ammoniac), dia- 
phoretic antimony (a combination of peroxide of antimony 
and potassa and alum)*\ Another method is to fuse 3 parts- 
of massicot (litharge) with 1 of antimony oxide, or to fuse 2 



INORGANIC PIGMENTS. 177 

parts of red lead, 1 of antimony and 1 of calamine (zinc 
carbonate). 

Brunner recommends slow fusion of 1 part of tartar 
emetic with two parts of lead nitrate and washing the ground 
melt with hydrochloric acid to brighten its colour. 

From these processes, which are evidently variations of 
one original method, it would appear that the pigment is a 
more or less basic antimoniate of lead with various impurities 
added according to taste. 

In his Cantor Lectures (1891) Mr. A. P. Laurie describes 
various pigments which have been included under the name 
of Naples yellow. We quote the section on this pigment, of 
lecture ii. : — 

** Griallolino. — The history and nature of this pigment are 
somewhat obscure. Cennino distinctly states that it is a 
volcanic product. He states that it is not a brilliant yellow, 
though brighter than ochre, and never makes bright greens. 
Mrs. Merrifield considers that several pigments were included 
under this name. I cannot do better than quote her sum- 
ming up of this matter. 

"1. 'A native mineral yellow pigment, known by the name 
of giallolino, giallolino di Napoli, jaune de Naples ^ luteolum Napo- 
litanum.' 

** This is doubtless the yellow referred to by Cennino. All 
trace of it seems to be lost, though probably a proper search 
in a volcanic district would lead to its discovery. 

** 2. *An artificial pigment which was composed of the 
yellow protoxide of lead, and which was called giallolino, giallo- 
lino finOy giallolino di fornace di fiandra, luteolum Belgictim genuU 
(the last is a Spanish term) and nmssicot, of which there are 
two varieties, namely, the golden or yellow, and the white or 
pale massicot.' 

" This pigment can be prepared by gently roasting white 

lead. It is now known as Turner's yellow. It is apt to turn 

12 




178 CHEMISTRY OF PIGMENTS. 

black, like all lead pigments, the fault of our towns, not of 
themselves. 

" 3. * An artificial pigment made at Venice, composed of 
giallolino fino and a certain kind of giallo di vetro, or vitreous 
yellow, for which a recipe is given in the Bolognese MS. in 
the Venetian dialect, and which appears to have been the 
Hornaza of the Spaniards/ 

" This recipe is worth quoting, and is as follows : — 

" * To make yellow glass for paternosters or beads : Take 
of lead 1 lb., of tin 2 lb. ; melt and calcine them, and make 
glass for paternosters. 

" * To make giallolino for painting : Take 2 lb. of this cal- 
cined lead and tin^ that is, 2 lb. of this glass for paternosters, 
2i lb. of minium, and J lb. of sand pounded very fine ; put it 
into a furnace and let it fine itself, and the colour will be 
perfect.* ^ 

" This pigment must have been a yellow lead frit. Prob- 
ably effective on fresco walls, but of little or no use in oil. 
Mrs. Merrifield then goes on : — 

*' ' I consider it established that they used two kinds of 
Naples yellow, namely : — 

*' * 1. A native mineral pigment found in the neighbour- 
hood of volcanoes, the nature of which is not accurately 
known, and which was called ** giallolino di Napoli " and 
*' jaune de Naples," and which is synonymous with the first 
kind of giallolino above mentioned. 

^' ' 2. An artificial pigment now in use (?) composed of the 
oxides of lead and antimony, called " giallo di Napoli," *' jaune 
de Naples," and Naples yellow, and which was not known to 
the old Italian artists.* 

" Apparently the manufacture of the more modern artificial 
Naples yellow has now ceased. I failed to find either that 

1 ♦* MS. of the fifteenth century in the library of the R. R. Ganonica Rego- 
lari, in the Convent of the S. Salvatore in Bologna." 



INORGANIC PIGMENTS. 179 

it was made or that any one had ever heard of its being made 
in Naples. The manufacture has long ceased, apparently. 
The colour now sold as Naples yellow is, I understand, usually 
a mixture of yellows. One sample I examined was massicot 
pure and simple. A fine yellow can be made from lead and 
antimony, and I have some here which I have made myself. 
Possibly a search on Mount Vesuvius might result in the 
rediscovery of the original Naples yellow." 

Arsenic Sulphides (Orpiment, Realgar). 

Of the three sulphides of arsenic AsgSg, ASgSg and As^S^ 
the first two are used as pigments, to some extent. They 
may both be formed artificially, or suitable specimens of the 
native mineral may be ground. 

Eealgar, Arsenic disulphide. — This occurs native as an 
aurora red or orange yellow mineral of the monoclinic 
system, of resinous lustre, transparent to translucent, of uneven 
conchoidal fracture. Specific gravity 3*4 to 3*6. It may be 
obtained artificially by fusing 75 parts of arsenic with 32 
parts of sulphur (it is probably better to use the proportions 
2:1 as loss of sulphur is likely to occur on fusion). It is 
distillable in a confined atmosphere but on heating in the 
air burns to AsgOg and SOg. 

Orpiment {Auri pigmentum, King's yellow, Royal yellow). 
Arsenic trisulphide. — Orpiment occurs in nature as a lemon- 
yellow substance found in foliated masses varying considerably 
in shade. Its specific gravity is about 3*4 to 3*5. It belongs 
to the orthorhombic system. 

It is usually prepared in the wet way by precipitating 
solutions of arsenious acid containing free hydrochloric acid 
with hydrogen sulphide — 

A82O3 + 3H2S = ASaSj + SHgO. 

It can also be prepared by fusing arsenic or arsenious 



180 CHEMISTRY OF PIGMENTS. 

acid with the proper proportion of sulphur. In the former 
case direct combination occurs, in the latter sulphur dioxide is 
formed. 

2A82O8 + 9S = aAajSj + 8S0a. 

The sulphide sublimes to the cooler parts of the vessel. 

Orpiment appears to be fairly permanent in oil though 
liable to be blackened when used in tempera. Both orpiment 
and realgar, being sulphides, .must be used with very great 
caution in admixture with other pigments. Mercury, lead 
and copper pigments should not be used in admixture with 
these colours. 

Cadmium Yellow, Radiant Yellow, Cadmium Sulphide CdS. 

Cadmium sulphide, which is a brilliant yellow substance, 
is used to a considerable extent as a pigment. It is usually 
prepared by the precipitation of a solution of a cadmium 
salt with hydrogen sulphide. In the case of the sulphate 

OdS04 + H2S = OdS + H2SO4. 

The bright yellow precipitate is collected, washed and 
ground. It is not entirely permanent, as will be seen on 
reference to Eussell and Abney's experiments already quoted. 
Cadmium yellow is also prepared by fusion of cadmium 
oxide with sulphur. 

Vandyck Brown. 

Vandyck brown is a name applied to various brown pig- 
ments owing their tints to either ferric oxide or organic 
matter (sometimes partially charred) or both. Church 
describes three varieties : " The first is made by calcining 
certain very ferruginous earths or brown ochres ; the second 
is nothing more than a dark brown variety of colcothar; 
the third is a kind of brown earth, containing, along with 
some iron oxide and hydrate, a good deal of organic sub- 
stance in the form of humus, or bituminous matter. The 



INORGANIC PIGMENTS. 181 

first and second kinds are permanent and innocuous, but 
the third kind will not resist the prolonged action of light, 
becoming paler and redder in course of time/* 

Prof. Church further states that most of the samples 
now met with in England belong to the third kind. 

We have examined some used for decorative purposes 
and found them to belong to the third class. The figures 
are given below. 

Dry Brown. Brown in Water. Brown in Oil. 

Moisture . . . 12-25 606 50-35 — 

Mineral matter . . 6-56 76 9-50 ^ — 

Organic matter . . 81-20 31-8 40*15 62-56 

Oil — — — 28-85 

Oxide of iron and alumina — — — 1-81 

Carbonate of lime, etc. . — — — 5*16 

Insoluble in HGl . . — — — 1-62 

10000 1000 10000 100-00 

Two samples of artists' colours were examined with the 
following results : — 

Oil 40-9 ^ 

Organic matter 38-5 J ®^'^ 

Oxide of iron 4*4 i 

Alumina 4-6 J ^^'"^ 

Lime salts, etc 5*4 3-9 

Insoluble in acid 6-2 2*9 

100*0 1000 

These are both rather organic than oxide of iron pig- 
ments and their permanence may well be a matter for doubt. 

^ Including 

Oxide of iron and alumina 3*00 

Carbonate of lime 4*05 

Insoluble siliceous matter 2*45 

9-50 



\ 



CHAPTEE IV. 

ORGANIC PIGMENTS. 

I PRUSSIAN BLUE. 

The pigment generally known as Prussian blue is a mixture 
of double cyanides of iron, although a definite single com- 
pound is known which has a claim to the name. In the 
process of manufacture on a commercial scale, however, it 
is impossible to prepare this pure compound, so that the 
pigment is invariably a mixture. In this sense, then, Prussian 
blue will be referred to in the sequel. Alone, or diluted with 
an inert white base, it forms a very valuable paint, known 
under the names Prussian blue, Paris blue, Antwerp blue, or 
Chinese blue. When genuine it should not be diluted, and 
under the above names one expects to receive the pure blue. 
Several fancy names have been introduced for the diluted 
pigment, and in estimating the value of these compounds it is 
hardly necessary to say that their value is directly proportional 
to the amount of the true pigment they contain. Prussian 
blue also forms the base, together with lead chromate, of the 
well-known Brunswick green paint. 

History, — The historical aspect of this important pigment 
is of some interest on account of the fact that that of the 
cyanogen compounds as a group may be said to have com- 
menced with the manufacture of Prussian blue. This was 
accidentally discovered in the early part of the eighteenth 



ORGANIC PIGMENTS. 183 

• 

century by a colour manufacturer of the name of Diesbach. 
He shortly afterwards communicated the fact to the chemist 
Dippel, who was an alchemist, and he carefully investigated 
the conditions under which the colouring matter was formed. 
Woodward first, however, published a method of making it. 
He stated that it was obtained by heating equal parts of 
cream of tartar and nitre, and heating strongly the resulting 
alkaline mass with ox blood. The residue of the calcination 
was then lixiviated, and green vitriol (sulphate of iron) added, 
together with alum. A greenish precipitate was thrown 
down, which on treatment with hydrochloric acid 3rielded the 
blue colour {Phil. Trans., 1724). Various other animal matter 
was soon shown to jielA the same result. It is unnecessary 
here to go into the various views which were in the early 
days held as to the constitution of the pigment, all of which 
were later proved to be erroneous. Macquer in 1752 showed 
that the use of alum was not necessary. The first real 
indication of its constitution was given by the last-named 
chemist, who showed that when boiled with alkali it yielded 
oxide of iron, leaving a new body in solution. To this sub- 
stance, which we now know as potassium ferrocyanide, the 
name phlogistigated potash was given. Towards the end of 
the eighteenth century Scheele investigated the compound, 
and the result was the discovery of that deadly poison, prussic 
acid. A few years later Berthollet took up the investigation, 
and to him and Guy-Lussac we owe our first real insight 
into the molecular constitution of the double cyanides. 

Before passing on to the study of the actual constituents 
of the commercial pigment, we may briefly examine the 
principles underlying the process of its manufacture. The 
production of the pigment is intimately connected with the 
manufacture of the well-known salt prussiate of potash (the 
yellow prussiate, potassium ferrocyanide), so that it is neces- 
sary to describe the manufacture of the latter. Animal matter, 



184 CHEMISTRY OF PIGMENTS. 

such as the shavings of hoofs, horn, dried blood, skin or 
hair, is used as the source of the carbon and nitrogen in the 
compounds. Owing to the large quantity of nitrogen these 
substances contain, they were sometimes calcined alone in the 
first instance in order to obtain as much ammonia as possible. 
Sufficient nitrogen, however, is retained for the production 
of the cyanogen required for the prussiate. The charred 
organic mass is mixed with potassium carbonate (this is 
preferably added in strong solution, and the water afterwards 
driven off). The mixture is then heated in a cast-iron retort, 
the iron necessary being taken up from this, or, as preferred 
by some manufacturers, scrap iron is added to the mass. The 
mass is then extracted with water and the water filtered off 
and boiled down. A series of recrystallisations is necessary 
to obtain the prussiate in a state of purity, and excess of 
carbonate of potassium should be avoided. For the manu- 
facture of ordinary Prussian blue, however, the crude solution 
is frequently employed, and it is only in the finer varieties 
that the pure crystals are first separated. Processes have 
been patented for the recovery of ferrocyanides from gas and 
soda liquors, and at least one of the large gas companies is 
now employed in the manufacture of Prussian blue. The 
blue pigment is obtained in many different shades, and the 
methods used are as variable in detail as is the composition 
of the resulting pigment. In general the principle of the 
process is the addition of either a ferric salt to the solution of 
the prussiate, or of a ferrous salt, the resulting nearly colour- 
less precipitate being treated with a suitable oxidising reagent 
such as nitric acid, ferric chloride, or bleaching powder. 
According to A. H. Allen the lighter shades are useful for 
the manufacture of zinc greens and the darker for the pre- 
paration of chrome greens. Gentele states that the best 
blues are obtained by using a ferrous salt and oxidising the 
ferrous ferrocyanide formed. In the process recommended 



ORGANIC PIGMENTS. 



185 



by Crowther and Eossiter the ferrous ferrocyanide is sus- 
pended in strongly acidulated water, and submitted to electro- 
lysis. A blue of extremely vivid violet reflex is obtained at 
the anode. 

Various allied compounds of iron and cyanogen, with or 
without potassium, are well known. These result from the 
treatment of ferrocyanide or ferricyanide with ferrous or 
ferric salts. In theory, one definite compound may be stated 
to result in a given reaction, but owing to the oxidation by 
the atmosphere, to impurities in the salts, and to other uncon- 
trollable circumstances, a mixture always results in practice. 
The following table gives the well-defined members of this 
series : — 



Compound. 


Formula. 


Common Name. 


Reaction between 


1. Potassio - ferrous- fer- 
ro- cyanide 

2. Potassio- ferric -ferro- 
cyanide 

3. Dipotassio - diferric - 
diferrocyanide 

4. Ferric ferrocyanide 

5 . Potassio - f errou s- f er- 
ri-oyanide 

6. Ferrous ferricyanide 


K^Fe^CeNe 

KFe^CeNe 

K2Fe4Ci2Ni2 

Fe^CigNis 

KFeaCfiNe 

Fe^Ci^Nia 


Everitt's salt 

Williamson's blue 

Soluble Prussian 

blue 
Prussian blue 

Williamson's blue 

Turnbull's blue 


Ferrous salts and 

ferrocyanide 
Ferric salts and 

ferrocyanide 
Ferric salts and 

ferrocyanide 
Ferric salts and 

ferrocyanide 
Ferrous salts and 

ferricyanides 
Ferrous salts and 

ferricyanides 



Which of these bodies, 2 or 5, actually represents Williamson's 
blue is not certain, but the two bodies are practically, if not 
actually, identical. 

For all practical purposes the blue sold on the market 
under the name of Prussian blue may be regarded as a mix- 
ture of iron and iron-potassium ferrocyanides. 

The Analysis of Prussian Blue. — Full details as to the 
methods of analysis of this important pigment were de- 
scribed by us in a paper published in the Analyst (September, 
1896), from which we quote the following description in full : — 



186 CHEMISTBY OF PIGMENTS. 

** We have found, and Dr. Williamson in every case found,, 
that alkali was present in so-called Prussian blue, not merely 
as alkaline salts not washed away completely, but as an in- 
tegral part of the cyanide. 

" As we are frequently called upon to examine commercial 
samples of Prussian blue, and of pigments containing this 
substance, we have considered it desirable to make a more 
complete examination than the method usually adopted would 
afford of specimens of blue of known origin, with a view to 
getting some more definite data for basing conclusions as to 
the purity of samples of unknown make. 

*' It appeared to us that, more especially in the case of com- 
plex pigments ground in oil, the determination of the nitrogen 
would give valuable information as to the amount of Prussian 
blue present. 

** Dyer has shown {Chem. Soc. Joum,, 1896, 811) that ferro- 
cyanides and ferricyanides yield the whole of their nitrogen 
as ammonia when treated by the Kjeldahl-Gunning-Arnold 
method. We found that potassium ferrocyanide boiled with 
sulphuric acid for a few minutes gave up all its nitrogen as 
ammonia. A determination of the water of hydration (lost 
at 180° to 200° C.) was also made. The results were : — 

Found. Theory. 

N 19-64 19-95 

HaO 12-79 12-71 

** We therefore felt justified in assuming that equally 
correct results would be obtained in the case of the allied 
compounds contained in commercial Prussian blue, an ex- 
pectation which was fully justified by the agreement of the 
nitrogen determinations with the other figures obtained. 

** The following is briefly the scheme of analysis adopted 
by us : — 

** The moisture is determined at 100°. The water of com- 
bination — if the term is here justifiable — can scarcely be 
determined unless the blue is * burned * and the water col- 



ORGANIC PIGMENTS. 187 

lected, as we made several attempts to drive off the water in 
a current of hot air, gradually raising the temperature until 
at 230° C, when water appeared to be still coming off, the 
pigment was decomposed with the formation of ferric oxide. 
Dr. Williamson, in his classical paper, * On the Blue Com- 
pounds of Cyanogen and Iron,* determined the total water 
in these pigments by combustion with plumbic chromate. 
This is apparently the only way of obtaining a correct result, 
as, on heating, part of the hydrogen is evolved as hydrocyanic 
acid, the oxygen of the water going to form ferric oxide, as 
stated. The nitrogen was determined as above described, 
and was found to differ within small limits. A weighed 
quantity was ignited, care being taken that the temperature 
was sufficiently high to decompose the last traces of the blue, 
but not too high to render the oxide of iron difficult of solu- 
tion. It is necessary to ensure the complete oxidation of the 
finely divided iron, as otherwise it is very difficultly soluble 
in hydrochloric acid. 

** In all cases on adding acid to the * ash,* a marked effer- 
vescence showed that alkaline carbonate (from the alkali- 
containing ferrocyanide) was present. Pure blue leaves an 
* ash ' completely soluble in hydrochloric acid, but in the 
case of adulterated Prussian blue or of diluted blues, barium 
sulphate or other insoluble matter must be filtered off and 
weighed before precipitating with ammonia. The iron in 
the (weighed) mixed oxides was determined by titration with 
potassium bichromate after reduction with stannous chlo- 
ride, the alumina being of course estimated by difference. A 
portion of the filtrate was evaporated to dryness, and, after 
volatilisation of the ammonium salts, the alkaline salts were 
weighed, and the chlorine therein determined by titration with 
silver nitrate. In another portion of the filtrate the sulphuric 
acid was determined, and from these data — viz., the weight 
of the alkaline salts, chlorine and sulphuric acid — we were 



188 



CHEMISTRY OF PIGMENTS. 



enabled to show that in all cases the alkah-metal was almost 
entirely potassium or sodium, and in no case a mixture of the 
two metals. Another weighed quantity of the pigment was 
boiled for a few minutes with aqueous potash, and the result- 
ing precipitate of oxide of iron weighed, after ensuring its 
complete conversion into Fc^Og. This, multiplied by 0*7, 
represents the * extra-radicle * iron. 

** The following tables represent the composition of eight 
samples of blue sold by makers of repute as genuine Prussian 
blue of good quality : — 

Composition of Eight Samples of Commercial * Pure ' 

Prussian Blue. 





I. 


II. 


III. 


IV. 


V. 


VI. 


vn. 


VIII. 


Moisture (lost at 


















100° C.) 


5-61 


3-54 


5-36 


5-45 


74-53 


5-32 


5-56 


5-61 


Water of combina- 


















tion, etc. 


15-46 


18-18 


6-22 


13-07 


3-08 


7-86 


14-60 


16-93 


Cyanogen i 


37-72 


41-10 


4-2-97 


87-90 


10-64 


39-91 


40-19 


40-86 


Iron 2 


29-48 


32-16 


34-27 


30-32 


7-97 


30-94 


31-94 


31-25 


Aluminium . 


1-82 


•52 




3-17 


■72 


1-00 


1-43 


1-52 


Alkali metal (Na) . 


7-60 


(K) 4-50 


(K) 7-72 


(K) 2-25 


(K) 106 


(K) 11-31 


(Na) 2-52 


-76 


Alkaline sulphate . 


2-31 
10000 


— 


3-46 


7-84 


'2-00 


3-66 


3-76 


(Na) 3-07 


100-00 


100-00 


100-00 


100-00 


100-00 


100-00 


100-00 


1 Nitrogen • . 


20-31 


2213 


2314 


20-18 


5-73 


21-49 


21-64 


22-00 


2 'Extra - radicle' 












1 




19-38 


iron 


16-66 


18-99 


1905 


16-04 




1 16-21 


18-98 



Composition of Drt Mattkr of above Samples (Dried 

AT 100° C). 





I. 


II. 


III. 


IV. 


V. 


VI. 


VII. 


vin. 


Water of combination, et<;. . 

Cyanogen i 

Irona 

Aluminium 

Alkali metal 

Alkaline sulphate .... 


16-38 

39-96 

31-23 

1-93 

8-05 

2-45 


18-85 

12-61 

33-34 

•54 

4-66 

100-00 


6-58 
45-41 
86-21 

8-16 
3-64 


13-87 

40-06 

.S2-05 

3-35 

2-38 

8-29 


12-03 

41-77 

31-30 

2-90 

4-16 

7-84 

100-00 


8^35 
42-14 
.32-67 

1-03 
11-94 

3-87 


15-46 

42-55 

33-82 

1-52 

2-67 

3-98 


17-95 

43-29 

3309 

1-61 

0-81 

3-25 


10000 


100-00 


100-00 


100-00 


100-00 


100-00 


1 Nitrogen 

' * Extra-radicle ' iron 
Intra-radicle iron (found) 
Intra-radicle iron (calculated 
from nitrogen) .... 


21-52 
17-65 
13-58 

14-34 


22-94 
19-69 
13-65 

15-30 


24-45 
20-02 
16-19 

16'30 


21-57 
16-95 
15-10 

14-38 


22^49 
14-99 


22-69 
17-12 
15-55 

15-12 


22-91 
20-09 
13-73 

15-28 


23-30 
20-51 
12-78 

15-54 



ORGANIC PIGMENTS. 189 

" In looking at these figures, it will be seen that the per- 
centages of iron and nitrogen do not vary greatly. The 
amounts of iron in the iron-cyanogen radicle, calculated frbm 
the percentage of nitrogen and from the difference between 
total and extra-radicle iron, do not agree closely in all cases. 
We can offer no explanation of this. Taking the figures for 
the dry matter, the greatest difference in iron was in the 
cases of III. and I., 4*98 per cent., and the greatest difference 
in nitrogen — between III. and I. again — 2*93 — differences 
which, calculated on the mean percentages, are under 16 
and under 13 per cent, of the totals respectively. 

** It will also be noticed that seven out of the eight samples 
contained aluminium. This is not to be considered as an 
adulterant, as alum is often added to the sulphate of iron 
used in precipitating the ferrocyanide without any idea of 
adulteration, but probably to cause the precipitate to settle 
better and to dry in a more coherent manner. It probably 
exists as aluminium ferrocyanide, a compound described by 
Tissier (Comp, rend.y xlv., 232). This has no colouring pro- 
perties, and, of course, the iron and nitrogen in the iron 
cyanogen radicle of this compound appear in the total iron 
and nitrogen as determined. If merely the ammonia precipitate 
is taken and called * ferric oxide,' the alumina is included 
as oxide of iron. 

** We think that the addition of alum to the precipitating 
tank is unnecessary, especially as the best sample of blue we 
have examined contained none. 

'* Alkali metal, as iron-akali cyanide, is present in every 
case. This agrees with the statement of Williamson and. 
others that a blue cannot be obtained free from alkali metal, 
except when hydroferrocyanic acid is substituted for alkaline 
ferrocyanide in the manufacture (the alkaline sulphate present 
in each case is, of course, due to imperfect washing). 

'* In fact, Prussian blue, if by that term we mean ferric 



190 



CHEMISTRY OF PIGMENTS. 



ferrocyanide Fe7(CN),8, is not known to the commercial 
world. Commercial Prussian blue is a mixture of William- 
son's blue with other iron-alkali cyanides, and often with 
almninium-iron cyanides, altogether a most complex sub- 
stance. 

*'An examination of the watery extract showed, in the 
cases of I. and VI., the presence of alkaline ferrocyanide. 
This is rather remarkable, as with the quantities usually 
taken the iron is in excess. We believe that these came 
from the same maker, but are sure, however, that both 
samples were sent out as hond-Jide Prussian blue. 

"The following notes on appearance of the samples in lump 
and in powder, depth of colour, etc., may be of interest : — 



Condition. 


Appearance. 


Powdered Samples. 


Classifica- 
tion in order 
of Depth of 
Colour. 


Quality 
of Tint. 


I. Lumps, conchoidal 

fracture 
II. Lumps 

III. Lumps, conchoidal 

fracture 

IV. Lumps, conchoidal 

fracture 
V. Paste 
VI. Lumps, conchoidal 
fracture 
VII. Powder 
VIII. Lumps 


Blackish copper glance, but; not 

a bright sheen 
Blue, pale-looking, no coppery 

glance 
Rich blue, bright coppery sheen 

Ditto, but not as good as III. 

Dried, with coppery lustre 
Blackish coppery glance, but 
not a bright sheen 

Light blue, no coppery glance 


2 
6 
4 
3 ' 

1 

7 
5 


6 
4 
1 
2 

7 

5 

8 



'* The mean percentage of iron in the dry matter of these 
eight samples was 3296. This would give 303 as the factor 
for calculating iron to Prussian blue. The mean percentage 
of nitrogen was 22*73 ; this would give as a factor for calcu- 
lating nitrogen to Prussian blue 4*4. The following tables 
show the accuracy to which these factors gave the percentage 
of Prussian blue in the eight samples examined : — 



OBGANIC PIGMENTS. 



191 



In Dry Matter. 


I. 


II. 


III. 


IV. 


V. 


VI. 


VII. 


VIII. 


N X 4-4 
Fe X 3-03 


94-69 
94-63 


100-93 
101-02 


107-58 
109-71 


94-91 
97-11 


98-95 
94-84 


99-83 
93-99 


100-80 
102-47 


102-52 
100-26 



'* Of course, these are merely empirical factors, based on 
the examination of commercial samples of varying composi- 
tion, and do not possess the accuracy of a factor to reduce 
one definite chemical compound to terms of another, but, at 
any rate, taken together they are of sufficient accuracy for 
calculating the percentage of Prussian blue in pigments 
containing that colour. The nitrogen alone in most cases 
would be sufficient. 

*' We feel justified in stating that blue sold as Prussian 
blue should contain at least 20 per cent, of nitrogen and 30 
per cent, of iron calculated on the dry matter, and, after 
burning, should be entirely dissolved by hydrochloric acid. 
A *dry' blue should certainly contaiii under 7 per cent, 
moisture. Another important point is that the sulphuric 
acid used in the Kjeldahl nitrogen determination should 
not be blackened. Pure cyanides dissolve in sulphuric acid 
without any charring, which, if it occurs, indicates the pre- 
sence of organic adulterants. A case of this kind will be 
noted later. 

*' The watery extract should not indicate the presence of 
excess of alkaline ferrocyanide. We consider that this is 
evidence of defective manufacture, although it cannot, of 
course, be regarded as adulteration. Still it — containing as' 
it does iron and nitrogen — is partly included in the analysis 
as Prussian blue, whereas it has no pigmentary value, and 
its solubility in water does not add to the weathering qualities 
of the colour. 



192 chemistry of pigments. 

"Commercial Pigments. 

" The following cases of examination of an adulterated 
sample of Prussian blue (of German manufacture) and of 
some colours ground in oil possess some interest. 

'* A rather pale-looking sample of dry powdered Prussian 
blue, which we were told was a cheap sample of German 
manufacture, gave only 14*35 per cent, of nitrogen. This 
at once aroused our suspicions, especially as, instead of be- 
coming colourless in a few minutes on boiling with sulphuric 
acid, a decided blackening occurred. This clearly pointed 
to the presence of an organic adulterant. On further exam- 
ination, the following figures were obtained : — 

Moisture 11-35 

Water of combination, organic adulterant, alkalies, etc. 37*76 

Cyanogen 1 26-65 

Iron 22-67 

Aluminium . . . 1*14 

Insoluble . -43 

100-00 

Per cent, nitrogen x 4'4 63-10 

iron X 3-03 68-69 

This sample not only contained more water than is usual, 
but was clearly deficient in blue. We think that one is 
justified in stating that it did not contain more than 70 per 
cent, of Prussian blue. 

'' Two samples of * celestial blue * gave the following 
results : — 

Dry. Ground in Oil. 

Prussian blue 7'12 6-29 

Barium sulphate 92-88 75*60 

Oil — 13-94 

Undetermined — 4-14 

" In the case of colours ground in oil, the Kjeldahl method 
is particularly applicable for the determination of nitrogen. 



1 



Nitrogen 14-35 



ORGANIC PIGMENTS. 193 

and, as now it is very general to sell these colours in oil 
instead of dry, we think that the nitrogen determination will 
be found a very convenient method of ascertaining (approxi- 
mately) the amount of Prussian blue in the many diluted 
colours made from it. Adulteration with nitrogenous matter 
is not probable, and so is not likely to lead to erroneous 
results. We intend to continue the examination of all samples 
which come under our notice by this method, which is rapid 
(we have obtained a result in under one hour), and at once 
points to any serious sophistication." 

Prussian blue occurs in commerce as amorphous lumps 
with a conchoidal fracture, and a strong coppery lustre, 
which varies much in different samples, the best samples 
showing a very strong lustre. It is so dark in this state 
that its real colour value cannot be judged whilst the pig- 
ment is in an undiluted condition. The actual value in this 
respect can best be judged by comparing a carefully ground 
mixture of 5 per cent, of a standard pure blue and 95 per 
cent, of white lead with a similarly prepared mixture of the 
given sample. More of the sample is added if necessary to 
equalise the two shades, when the colour values are in the 
inverse ratio to the amount of blue present in the mixtures. 

Commercial samples, especially cheap German blues, are 
often adulterated with barium sulphate, gypsum, chalk or 
occasionally starch. Some very carelessly prepared samples 
which have a very poor appearance are coated with a well- 
prepared blue, so that it is necessary to make more than a 
superficial examination. The adulterants usually met with 
can be detected in the ordinary manner, and if the sample 
be examined in the manner we have above described any 
sophistication vnll be revealed. 

Although largely employed, and of great value, Prussian 

blue is not quite permanent in its nature. This is much 

more marked in badly prepared samples, so that any Prussian 

13 



194 CHEMISTRY OF PIOMENTS. 

blue employed for artists' work should be of the highest 
possible quality. 

We have again recently come across samples of Prussian 

■ 

blue which contained free potassium ferrocyanide. This is 
clearly due 'to imperfect washing, and in every case the pig- 
ment was very poor in colour, and when diluted with a 
white base more closely resembled a French grey than a 
good blue. 

One of these had the composition — 

Moisture 3*71 

Prussian blue 89*29 

Water-soluble matter (alkaline f erro or f erricyanides) 7"00 



10000 



The presence of so much ferrocyanide is not only evi- 
dence of incomplete washing, but also clearly shows that 
ferric chloride was not used as an oxidising agent for the 
Everitt's salt. The finest colour we have examined was 
one prepared by oxidation with this reagent. 

Two samples of Prussian blue, ground in oil, had the fol- 
lowing composition : — 



Oil 


9-96 


24-61 


Prussian blue .... 


42-24 


26-00 


Calcium carbonate, etc. 


25-80 


27-13 


Insoluble in acid (BaS04) 


22-00 


22-26 



10000 100-00 

These more closely' approximate in composition to Antwerp 
blue, and it is certainly undesirable that such substances 
should be sold as Prussian blue without some qualifying 
description. 

11.— NATURAL LAKES. 

This important group of pigments may be regarded as 
compounds of some animal or vegetable colouring matter 
with an inorganic base. The usual metallic base employed 



ORGANIC PIGMENTS. 195 

in their preparation is alumina, or a mixture of that body 
with lime, magnesia or oxide of iron. 

The old-fashioned lakes were prepared from such sources 
entirely, the colour being derived from either an insect, such 
as cochineal, or a plant such as logwood. To-day, however, 
lakes are prepared from the coal-tar colouring matters, and 
thus differ from the older lakes in the fact that their colour 
principle is of artificial origin. Although frequently of very 
beautiful colour, the lakes as a class suffer from one common 
objection, which restricts their use, namely, the fact that 
they are not permanent to light. They were used in very 
early times, the Italian artists being very fond of them. 
The origin of this class of colouring matters is said to be 
as follows : In the early days of Italian dyeing, a colouring 
material was used which was known as "lac". In the 
process of. dyeing it was necessary to use a substance as a 
mordant to develop and fix the colour on the fibre, and 
salts of aluminium and tin were soon found to be the most 
suitable for the purpose. During the process, combination 
naturally took place in the vat liquid itself as well as on the 
actual fibre. As a result the insoluble compound of colour 
and base, which was of a very voluminous nature, floated to 
the surface in the form of a scum. This was collected and 
dried, and then sold to artists under the name of lacca. 
This special name soon became generic, as other colours 
were found to yield similar compounds, and so the name 
passed into common use. As would be expected, in certain 
well-defined cases the natural colouring matter is of an acid 
nature, which accounts for its ready combination with bases. 
This will be referred to in more detail in the sequel, but at 
the present moment it may suffice to say that a '* theoretical " 
lake would consist of a compound between the acid and the 
base in molecular "proportions : such theoretical lakes, how- 
ever, have no practical existence, and often a series of lakes 



196 CHEMISTRY OF PIGMENTS. 

of a given colour exists, in which the tint depends entirely 
on the proportion between the acid and the base, part of 
which is in chemical combination, and part in a kind 
of mechanical mixture. Although the processes used for 
the preparation of these colours vary very much, and are 
often carefully kept secret, the principle underlying their 
preparation may be illustrated in the following example. A 
decoction of the natural substance in water is prepared of as 
high a strength as possible, and after filtering it from sus- 
pended particles, a solution of the base is added to the liquid. 
The exact conditions under which the base is added deter- 
mine the resulting tint, and it is in a scientific appreciation 
of these conditions that success depends. Some natural 
colouring matters exist ready formed in the plant, etc., and 
yield lakes which do not greatly differ in colour with the 
nature of the base used : whilst others do not exist as 
colours in the fresh plant, but are only developed when the 
base is added, and therefore differ greatly in the resulting 
colour of the lake, according to the nature of the base used. 

Cochineal Lakes. 

The Spanish conqueror, Cortes, and his comrades found 
the cochineal insect used in Mexico ; and Prescott, the able 
historian of the conquest, seems to be definitely of the opinion 
that this was the first cause of the introduction of this colour 
into Europe. 

The coccus used in Europe and Asia Minor was probably 
an insect, kermes, attacking the kermes oak (Quercus 
coccifera). 

The beautiful colouring matter known as carmine, with 
its various lakes, is derived from the insect. Coccus cacti. 
The variety usually employed appears to be the dried fecun- 
dated female insect which has been reared on various species 
of Nopalea. It has been stated that so long ago as in the 



ORGANIC PIGMENTS. 197 

time of Moses a red colour was derived from an insect, and 
used for dyeing the high priest's garment. This appears to 
have been some species of Coccus, probably identical with the 
Coccigranum of Pliny. The male insect does not furnish the 
colour. 

It is true that this colour does not find a very extensive 
use except for a few special purposes, save in the dyeing 
industry. Its value as a pigment is greatly diminished on 
account of the action of hght, possibly combined with .that 
of moisture. Outside work in carmine colours, whilst being 
at first very beautiful, is not at all lasting. Further, it is 
naturally much more expensive than most reds, so that its 
use would be limited on that account alone. 

The following preparations of this colour are, however, 
of sufficient interest and importance to justify their being 
shortly described. 

Carmine. 

It is uncertain when this beautiful pigment was discovered, 
but the earliest recipe that can be traced is one given by 
Homberg in 1656, when it was already a well-known colour. 
According to Wiegler (Die natilrliche Magie, published in 
Berlin in 1782) it was accidentally discovered in Florence 
or Pisa by a Franciscan friar. It was said to have been 
thus found by chance during its use in the preparation of 
some medicine, in which form it had for some time enjoyed 
a reputation. Its name has even been derived from the 
same root as '* carminative " by enthusiastic etymologists, 
assuming that its use in medicine was of this nature. 

It may be regarded as the highest lake of the series to 
which it belongs, that is, it is the nearest approximation to a 
true compound without excess of base. The methods used 
in its preparation are varied, and have in most cases been 
kept as secret as possible. The following are some of the 



198 CHEMISTRY OF PIGMENTS. 

published methods, but they must be accepted with reserve, 
as in many cases misleading information has purposely been 
published. 

(1) One pound of crushed cochineal insects are boiled in 1 
gallon of water for a quarter of an hour, and 1 oz. of ordinary 
alum added, the boiling being continued for a short time 
longer. After standing for a few hours the clear supernatant 
liquid is decanted, and this after a few days deposits about 
an ounce and a half of carmine. A crop of an inferior nature 
is deposited after a short interval. The addition of a little 
cream of tartar is said to assist in the deposition of the 
carmine. (2) Two pounds of the insects are boiled with 
water, and to the clear decoction, 2 oz. of alum and 3 oz. of 
a saturated solution of stannous chloride with 2 oz. of sodium 
carbonate are added, and the liquid allowed to stand for a 
time until the carmine is deposited. (3) The following 
method is the subject of a patent, dated 1856 : 9 oz. of car- 
bonate of sodium, 8 oz. of citric acid and 27 quarts of water 
are boiled together, a pound and a half of insects are added, 
and the whole again boiled for an hour and a half. The liquid 
is then strained and clarified. The clear solution is then boiled 
and 9 oz. of alum are added. After again boiling for five 
minutes, the fluid is allowed to stand, until the carmine is 
gradually deposited, when it is collected, washed and dried. 
Without suggesting that these methods will give the best 
results, it is riot too much to say that they embrace the 
general principles underlying the successful preparation of 
carmine. 

Pereira, about fifty years ago, stated that alum was no 
good as a precipitant for carmine, but that such a substance as 
chloride of tin must be used. This however is not in accord- 
ance with almost universal experience, since alum is found to 
be the base of most of the fine commercial carmines. 

Carmine is a fine deep scarlet powder, of somewhat 



ORGANIC PIGMENTS. 199 

variable tint, according to its quality, but always of a brilliant 
fiery brightness. The best quality of commerce is known as 
*'nacarat carmine'*. It is insoluble in all the udual organic 
solvents, but is soluble in ammonia and the caustic alkalies. 
As a pigment it works well in oil or water, but is not per- 
manent to light and air. 

The Analysis of Carmine, — The moisture should be deter- 
mined in the sample, and, so long as it is pure carmine, the 
value is of course proportional to the amount of dry pigment 
it contains. As a general rule, one does not expect to find 
more than from 15 to 18 per cent, of water in commercial 
samples. Over 20 per cent, may be regarded as an unfair 
addition. The ash should not only be determined, but i<| 
should be as fully examined as possible. The bulk of it 
should be alumina and lime, and there should be no insoluble 
white pigments present such as barium sulphate or siliceous 
matter. To determine whether excess of base in the un- 
combined state is present, the sample should be exhausted 
with dilute ammonia, which removes the true compound, 
and leaves the uncombined alumina and lime, together with 
some organic matter. Valuable information in regard to 
the colouring matter itself is obtained by boiling a few wool 
fibres for half an hour in the ammoniacal solution : aniline 
scarlet dyes a red-orange tint, whilst carmine gives a distinct 
purple red. 

The presence of lakes of Brazil wood may be detected by 
dissolving the sample in the minimum quantity of very dilute 
ammonia and precipitating the carmine colour with excess 
of lime water. If Brazil wood lake be present, the filtrate 
after this treatment will have a purple or violet colour, as the 
colouring matter is not precipitated under these circum- 
stances. A compound of Biebrich scarlet with salts of tin 
resembles pure carmine closely in colour and in general 
characters. If tin be present in the colour, this body should 



200 



CHEMISTRY OF PIGMENTS. 



be looked for. It may be detected by boiling white wool in 
the ammoniacal solution of the colour, when, if the scarlet 
be present, the fibre assumes a red-orange colour, instead of 
a pure red purple. 

Dechan has given the following table of analyses of 
a number of commercial samples of carmine (Pharm. Journ., 
3, xvi., 611) : — 





I. 


II. III. 


IV. 


V. 


VI. 


VII. 


VIII. 


IX. 


Moisture 


22-1 


161 


20 


22-3 


20-2 


23-6 


100 


21-2 


130 


Colouring matter . 


46-1 


69-2 


34-1 


65-7 


60-8 


69-5 


72-0 


18-4 


67-5 


Alumina and lime, 




















etc. (dissolved by 




















ammonia) . 


8-0 


9-8 


11-4 


12-0 


90 


7-0 


8-1 


4-4 


10-0 


Organic matter (in- 




















soluble in am- 














* 






monia) 


21-8 


2-5 


18-5 




9-8 




8-0 


52-4 


9-5 


Ash (insoluble in 




















ammonia) . 


20 


2-4 


34-0 


trace 


0-2 


trace 


1-9 


3-6 


trace 



Carmine is met with in commerce, adulterated with 
various aniline colours and occasionally vnth such substances 
as starch. Excess of mineral matter, generally uncombined 
alumina, is also met with, and according to Dechan (Pharm, 
Journ,, 3, xvi., 511) there are also found vermilion and 
chrome red. These adulterations are, however, we think, 
almost apocryphal. 

Lafar (J. prak, Ghem., xliii., 130) has made a full analysis 
of a very fine sample of carmine (nacarat-carmine) and gives 
the following as his results. It contained 15*5 per cent, of 
water, 6'87 per cent, ash, 23*26 per cent, of nitrogenous 
matter and 52*37 per cent, of colouring matter. The com- 
position of the ash was as follows : — 

Cupric oxide 0*35 

Stannic oxide 0*14 

Alumina 40*48 

Calcium oxide . 44'20 

Magnesia 0*61 



ORGANIC PIGMENTS. 201 

Sodium oxide 5*40 

Potassium oxide 3*20 

Phosphoric acid 2'71 

Silica 0-60 

Carbonic anhydride 2*31 

Ferric oxide traces 

In this, as in most cases, the ratio of the alumina to the 
lime and magnesia is practically that of one molecule of the 
former to two molecules of the latter. A very high-class 
sample examined by Liebermann was found to contain 17 
per cent, of water, and yielded 3'7 per cent, of nitrogen, 
which may be taken as equivalent to about 23 per cent, of 
nitrogenous matter. The dry carmine contained 8*1 per cent, 
of ash, the composition of which was as follows : — 

Stannic oxide 0*67 

Alumina . . 4309 

Lime 44*85 

Magnesia 1*02 

Sodium oxide 3*23 

Potassium oxide 3-66 

Phosphoric acid 3*20 

Neither the alumina nor the lime is precipitated from 
an ammoniacal solution of carmine by any of the usual 
re-agents, it being necessary to examine the ash to detect 
these metals. 

Although the chemistry of the cochineal dye had been the 
subject of researches by John (1813), Pelletier and Caventou 
(1818), and by Preisser and Arppe, the earliest systematic study 
of the body may be regarded as that of Warren de la Eue, in 
1847. He did not succeed in preparing the acid in a crystalline 
condition, and the formula which he assigned to it, C14H14O8, 
must now be regarded as incorrect. Schutzenberger (Ann, 
Chim, Phys,, liv., 62) arrived at the conclusion that De la 
Hue's acid was a mixture of several bodies, and assigned to 
the pure acid the formula C^HgOQ. Schaller later (1864) 
analysed what he believed to be pure carminic acid and 



202 CHEMISTRY OF PIGMENTS. 

assigned to it a formula differing from that of Schutzen- 
berger's, only by containing one molecule more of water. 

Hlasiwetz and Grabowsky {Annalen, cxli., 329) considered 
that carminic acid was a glucoside which yielded on hydroly- 
sis a sugar and carmine red. Von Miller and Eohde, however,, 
showed that this was not correct, as carminic acid did not 
alter on boiling with dilute sulphuric acid. 

These chemists originally held the view that the acid was 
a naphthalene derivative, but have since modified their opin- 
ions. They consider that the formula of carminic acid is 
either C24H22O14 or G22H20O13. 

The most modern researches, and those which are to be 
regarded as the most reliable, are those of Liebermann and 
of Schunck and Marchlewski. 

Liebermann, who has recently devoted much attention 
to the chemistry of the cochineal dye, considers that carminic 
acid is an indene derivative of the formula C22H22O13. The 
acid, which is easily soluble in water, readily passes into in- 
soluble colouring matters, the change being accompanied by 
elimination of water and increase 'of molecular complexity. 
This change is characteristic of the bodies of the ketoindene 
series. On oxidation by potassium persulphate, the dye 
yields two other acids. These have been termed coccinic 
acid, CgHgOg, a body very soluble in alcohol, but nearly in-^ 
soluble in water, melting at 293° with decomposition: and 
cochinelic acid, GioHgO^, which forms crystalline needles 
melting at 224° to 226°. It is moderately soluble in cold water^ 
and' easily so in alcohol. The former of these acids has been 
identified with the well-defined compound, hydroxy-uvitic 
acid. A study of these acids and their derivatives has led 
Liebermann to assign, provisionally, to carminic acid the 
constitution 

GOGH, CgH, GHgrGH), CH, OH 

I I 

CH(GH) -•GH(GH). 



OKGANIC PIGMENTS. 203 

Schunck and Marchlewski prepare pure carminic acid by 
treating cochineal extract with lead acetate, decomposing the 
lead salj with sulphuric acid in the presence of alcohol, and 
evaporating the liquid to dryness at the lowest possible 
temperature. The residue can be purified by dissolving in 
alcohol and precipitating with ether or benzene. It is then 
recrystalhsed from alcohol, when it forms small red prisms. 
Aqueous solutions of carminic acid, when evaporated, give an 
amorphous residue, but no crystals. According to Schunck,. 
carminic acid possesses the formula CiiHi20g or CnHgO^ 
with two molecules of water of crystallisation. His prepara- 
tion darkened at 130° and blackened without melting at 205*'. 
In alcoholic solution it shows three ill-defined absorption 
bands, one in the green and two in the blue. The barium 
and calcium salts are brown, changing to violet with excess 
of base ; the lead and aluminium salts are also violet, and 
the stannous salt scarlet. An aqueous solution is at once 
decolourised by animal charcoal, the latter increasing in 
volume and becoming gelatinous. This mass seems to be a 
compound which is not changed by alcohol, but is decomposed 
by alkalies. The anilide of carminic acid is deposited in ruby 
crystals from its solutions^ and melts with decomposition at 
189° to 190°. 

Crimson Lake. 

This pigment, which produces very beautiful results, is a 
more fully saturated lake of the colouring matter of cochineal 
than ordinary carmine. It suffers from the same defect as 
the last-named colour, namely, lack of permanency, so that 
its employment is somewhat limited. Much of the so-called 
crimson lake of the present day, however, is not a true 
cochineal colour at all ; this is especially true of the pigment 
when used in oil, it then being generally supplied by the 
artists' colourmen of repute, made from the coal-tar product,. 



204 CHEMISTRY OF PIGMENTS. 

alizarin. When so made it has the advantage of being pretty 
permanent, but in chemical constitution it must not be con- 
founded with the true crimson lake. When supplied as a 
water colour, it is generally made from the insect. 

Crimson lake may be regarded as a more basic compound 
of carminic acid than ordinary carmine, with, of course, more 
or less foreign matter present as well. The following receipt 
has been given as producing a very fine shade of this exquisite 
colour : Twenty parts of the powdered insects are boiled 
with 400 parts of water and ten parts of cream of tartar. 
After filtration, a solution of 300 parts of alum and a small 
quantity of stannous chloride are added to the solution. The 
precipitate first formed is exceedingly brilliant, but the 
greater part of the colour is still in the solution. To effect 
its precipitation a solution of carbonate of sodium is cautiously 
added, when the alumina is completely precipitated, along 
with all the colouring matter. One can hardly fix any 
standard for the quahty of this pigment, but it is necessary 
that it should be the product of the true cochineal, and it 
should, after allowing for the greater proportion of mineral 
matter, correspond closely in its behaviour with genuine 
carmine. 

The following recipe is given by A. P. Laurie (Cantor 
Lectures, 1891) as from a MS. in the Library of the Univer- 
sity of Padua, dated probably the middle of the seventeenth 
century. 

** ' To make a most beautiful purple lake, — Take an ounce of 
fine grana or cochineal, a quarter of an ounce of roche alum, 
and about a bocale full of common water. Boil the water 
with a quarter of an ounce of fennel seed until it is diminished 
one-third ; then add the grana or cochineal finely pulverised, 
and boil the whole over a slow fire for a quarter of an hour ; 
then add the pulverised roche alum, and let it boil for another 
quarter of an hour. After this, take it from the fire, strain it 



ORGANIC PIGMENTS. 205 

through a linen cloth into a new and unglazed earthen por- 
ringer, and leave it there for eight days. You must then decant 
the water, or take it up gently with a sponge, evaporating the 
little which remains, until the colour is condensed, which 
you must afterwards keep in shells, adding to it a little lemon 
juice. 

Mr. Laurie says : "I have tested this recipe, and find 
that a precipitate is thrown down of a purple colour. The 
addition of lemon juice referred to here, and in some other 
recipes, causes the lake to become more of a crimson and less 
of a purple." 

Lac Dye Lake. 

The substance known as lac dye is the product of Coccus 
lacca, an insect which lives on the banyan and other trees, 
especially those belonging to the genus Ficus. From the 
mature impregnated female insect a resinous exudation flows, 
which encloses the deposited ova. The twigs with the 
attached resinous matter and enclosed animal substance are 
broken ofif, and constitute stick lac. If the resinous mass 
be extracted with water, the greater part of the colouring 
matter present is dissolved, and the residue is known as seed 
lac, which when melted and strained and thus purified is 
sold as shellac. The colouring matter, or lac dye, is appar- 
ently prepared by treating the stick lac with a weak alkaline 
solution, and probably with a mixture of alumina and lime 
salts. It is used to only a very small extent now, and at 
most is only employed for pigmentary work in rare cases as 
an artist's colour. 

The composition of this colour has been investigated by 
Schmidt (Joum. Soc. Dyers, etc., iii., 122), who called the 
chief constituent laccainic acid, and pointed out its close 
resemblance to carminic acid. He assigned to it the formula 
CiftHigOg, and described it as a brown-red crystalline powder 



206 CHEMISTRY OF PIGMENTS. 

melting at 180°. It is soluble in alcohol and acetic acid, and 
to a fair extent in water. It is almost insoluble in etJaer. 

It appears to be a dibasic acid, and the chief difference 
between it and carminic acid is the difference in the absorp- 
tion spectra when dissolved in sulphuric acid. The two 
following analyses are given by Schmidt of two samples of 
the dye. 

Moisture 9*0 11-26 

Mineral matter 15*7 18*24 

Colouring matter 10*4 13*2 

Other organic matter 64*9 67'3 

A good lac lake is prepared by the use of alum as a pre- 
cipitant, and tin is also a good base when a fine colour is 
required. Samples of lac lake usually contain about 50 per 
cent, of colouring matter, 40 per cent, of resin, and 10 per cent, 
of alumina or of alumina and lime mixed. 

Colours prepared from this dye are rather more permanent 
than those from cochineal. 

Scarlet Lake. 

This pigment used to be a mixture of crimson lake with 
more or less vermilion. The fugitive nature of the cochineal 
colour, however, has caused it to be replaced very generally 
by an alizarin colour. It thus becomes practically a per- 
manent pigment. 

Madder Lakes. 

At one time the madder lakes were very largely employed, 
and held in very high esteem. Their value has in no wise 
diminished, but as the chemistry of the constituents of the 
root became more and more understood until finally artificial 
alizarin was an accomplished fact, the use of the natural 
product gradually diminished, until to-day it is almost 
entirely superseded by the artificial colours. Hence the 



ORGANIC PIGMENTS. 207 

following short epitome of the chemistry of the madder lakes 
becomes of little but historical interest. The root of the 
madder plant {Bvhia tinctorium) contains a considerable 
quantity of the colouring principle aUzarin (g.v.) in the form 
of a glucoside which is known as ruberythric acid. This 
body has the formula G^^^^^w ^^^ under the influence of 
either natural ferments or of dilute acids or alkalies it splits 
up into alizarin and the sugar, glucose. The equation repre- 
senting this change is as follows : — 

CaeHagOu + '23^0 = 2Cf,B.^fi^ + 0i4H«O2(OH)2. 

The closely allied body purpurin (q.v.) occurs in the root in a 
similar condition. 

The employment of madder has usually been in the form 
of a madder extract or of garancin, or garanceaux, the 
corresponding substance prepared from madder which has 
been once used and still contains some of its colouring matter. 
Garancin, obtained by treating the root with strong sulphuric 
acid, has been more frequently employed for the preparation 
of madder lakes than any other substance, and the following 
are the outlines of several processes which may be said to 
cover the general principles involved. Of course the details 
have been varied without limit, and lakes of different shades 
obtained accordingly. Khittel many years ago described the 
method he employed, in the following manner. One part of 
garancin is steeped in a solution of one part of sodium 
sulphate in thirty-six parts of water, and after a time is 
washed and pressed until all traces of the sulphate are 
removed. The purified garancin is then ready for use. A 
quantity of alum, free from the least traces of iron (which 
darkens the resulting lake very much), equal in weight to the 
garancin employed, is then dissolved in ten times its weight 
of water, and boiled. The purified garancin is then added to 
this solution. The mixture should not now be boiled, as the 



I 



208 CHEMISTRY OF PIGMENTS. 

resulting lake is darkened by too much heat. After about 
half an hour, with repeated agitation, most of the colouring 
matter is extracted. The liquid is then filtered from the 
residue, and when the filtrate has cooled to about 45° C. 
sub-acetate of lead is added in quantity equivalent to the 
amount of alum used. On stirring the mixture sulphate of 
lead is precipitated and rapidly subsides. The clear liquid is- 
then decanted before it has time to cool. It is then heated 
for some time to nearly the boiling point, and then the first 
fraction of the lake separates. This is of a very fine red tint. 
After the first bright red lake has been deposited, the residual 
liquid is divided into two equal portions, and to one is added 
ammonium carbonate until a slight turbidity is apparent. 
The two portions are now again mixed, and again heated^ 
when a fresh quantity of lake separates, which is not, however^ 
so brilliant as the first fraction. Great care must be employed 
in drying these lakes, as heat injures them considerably. 

Sace described the following method of obtaining a fine 
lake. He mixes 100 parts of an alcoholic extract of madder 
with 50 parts of water, and allows the mixture to macerate 
for twenty-four hours. More water is then added, and the 
solution is separated from the solid residue by straining 
through a silk sieve. A boiling solution of alum, containing 
10 per cent, of the salt is then gradually added until pre- 
cipitation takes place. TW^lake has a fine deep-red tint. 
By using sulphate of iron an almost black-violet lake results,, 
whilst alum containing a little iron yields intermediate colours. 

Kopp treated the root in powder with a solution of 
sulphurous acid and allowed the mixture to macerate for a^ 
time. The hot filtered liquid is then treated with a solution 
of aluminium acetate, or alum mixed with carbonate of sodium,, 
and the lake precipitated in fractions. The finer tints are 
deposited first, the later fractions containing more and more 
of the accompanying impurities. 



OBGANIC PIGMENTS. 209 

The high value of the natural madder lakes caused them 
to be often adulterated with cheaper colouring matters. The 
following description of the methods used for detecting the 
more usual adulterants is given by Chateau, and is repro- 
duced from an interesting old treatise, On the Manufactv/re 
of Colours by Malepeyre. We give an account of the 
methods, but are unable to vouch that by following the 
directions there given one will be able to detect all the 
admixtures that may be present, although good indications 
of the purity of the lakes can undoubtedly be obtained in this 
manner. 

** Bed and Pink Lakes of Madder. — These lakes do not colour 
water, either hot or cold. They colour ether and alcohol only 
very slightly, and only after some time. By calcination they 
leave a residue of alumina. 

*' Santaline. — If the lake be dark it may contain santaline, 
the colouring matter of red sanders wood {Pterocarpus santa- 
linus), which is detected by the orange-red colour acquired 
by the ether digested with the suspected lake. Alcohol under 
the same circumstances would be coloured red. 

'* If the lake be of a pink hue it may be falsified by lakes of 
Brazil wood or with (common) cochineal lakes. But as 
madder lakes and, generally, all lakes are insoluble in water, 
alcohol and ether, their colouring matter should be isolated, 
and the following method is proposed. Every lake with 
alumina for its base is soluble in hydrochloric acid, or in 
acetic acid to which a few drops of the former have been 
added, or in a solution of stannous chloride. After the lake 
is dissolved, ether is added to the solution, and the whole is 
shaken. All the colouring matter is dissolved in the ether, 
which will acquire the colour of the matter forming the basis 
of the lake. 

** Lakes of Brazil Wood. — If the lake be mixed with a lake 

of Brazil, Pernambuco or Japan wood, the colouring matter 

14 



210 CHEMISTRY OF PIGMENTS. 

will be dissolved in the ether by the above process, and the 
ether will be of a golden-yellow colour. 

'' Venice Lake. — This lake, one of the finest of the Brazil 
wood lakes, will disengage ammonia if heated in a test tube 
with a solution of potash. A pure madder lake does not 
yield any ammonia under these circumstances. 

" Carmine Lake, — ^Water will be coloured if cochineal lake 
is present, and the colour is intensified by heating. Aqueous 
solutions containing cochineal lake become violet when soluble 
alkalies are added, and give a violet precipitate with lime 
water, stannous chloride or zinc salts. Cochineal lake is 
turned a cherry red by stannous chloride, and the solution 
stains paper. Madder lake does not' behave in this manner. 

" Gampeachy Lakes, — In the presence of these lakes the 
addition of hydrochloric acid produces a crimson red colora- 
tion. When extracted with ether as above mentioned, the 
ether will be of a golden-yellow colour, which yields the 
crimson red reaction with hydrochloric acid. 

" Alkanet Lakes, — The lake is dissolved in acetic acid and 
the solution extracted by carbon bisulphide. If alkanet be 
present, the carbon bisulphide is coloured an intense violet 
red. This is characteristic of this colouring matter. When 
heated, the lake gives off violet fumes if alkanet be present. 
After dissolving the lake in acetic acid, and separating the 
colour with ether, this is evaporated, and the residue is 
treated with alcohol, which dissolves the colouring matter of 
alkanet. The alcoholic solution gives a blue precipitate with 
lead subacetate solution. 

*' Orchil, — If orchil colouring matter be present, the colour 
is yielded to hydrochloric as a deep red. If this solution be 
shaken with ether, the orchil does not yield the least colour 
to that solvent. 

*' Prussian Blue. — In the case of this somewhat rare adul- 
terant, the lake will be of a violet colour. This will be 



ORGANIC PIGMENTS. 211 

changed to a green by hydrochloric acid, and the iron cyanide 
compounds can be recognised and determined by the usual 
methods (see Prussian Blue)." 

Alizarin Lakes, 

The chemistry of this group of pigments is now of very 
great importance, since the alizarin colours have practically 
replaced the madder colours for dyeing purposes, and have 
of recent years become of great importance as pigments for 
certain kinds of work. In the dyeing industry they are 
always employed in such a manner that they yield lakes as 
the resulting compound, so that ahzarin dyes differ but little 
in theory from alizarin pigments. 

Alizarin may be described as an anthracene derivative, 
and as the number of colouring matters derived from this 
coal-tar hydrocarbon is very limited, and since they all resemble 
each other very closely in their chemical properties, the an- 
thracene group may be looked upon as an isolated and naturally 
related series of coal-tar colours. 

They are of a strongly acidic nature, which explains the 
fact that they form admirable lakes, and in dyeing they can 
only be used in conjunction with mordants, or, in other words, 
can only be employed in the form of lakes. They possess 
the advantage of being very permanent to light, far more so 
than most coal-tar colours, and they are also very fast on 
fibres when used as dyes. 

Commercial alizarin. — The hydrocarbon anthracene is usu- 
ally transformed into alizarin by means of three distinct 
operations. It is first oxidised to anthraquinone by means 
of chromic acid, and the resulting body is treated with sul- 
phuric acid in order to convert it into a mixture of sulphonic 
acids. These are melted in the last stage of the process with 
caustic soda, when alizarin is produced. These steps in the 



212 CHEMISTBY OF PIGMENTS. 

transformation are illustrated by reference to the following 
diagrammatic formulae : — 

/OHv /COv /C0> 



\CH/ \C0/ ^CQ/ 

Anthracene Anthraquinone Anthraquinone 

di-Sulphonic Acid 

\co/ 

Alizarin 

Alizarian is, chemically, 1:2: dioxy-anthraquinone. It 
forms orange-red needles melting at 290°, and subliming at 
higher temperatures. It is identical with the principal colour- 
ing matter of the madder root (Bubia tinctorium), in which 
it occurs as a glucoside known as ruberythric acid (identical 
with morindin, from Morinda citrifolia). 

Of the trioxy-anthraquinones, of which a number are 
known, the most important are purpurin, flavopurpurin and 
anthrapurpurin. These are all isomeric bodies related to 
alizarin by having one of the hydrogen atoms (different in each 
case) replaced by an OH group. 

Alizarin, Ci4Hg02(OH).2, is prepared in the pure state by 
melting pure anthraquinone-monosulphonic acid with caustic 
soda. It can also be obtained from ordinary blue shade 
commercial alizarin paste in the following manner. The 
paste is dissolved in caustic soda, and the solution filtered. 
A solution of barium chloride is added, and the whole is 
heated to boiling point, when the barium compound of alizarin 
separates out in a crystalline condition. This is collected on 
a filter and washed, and finally decomposed by an acid. It 
can be freed from the last trace of impurities by recrystallisa- 
tion from glacial acetic acid or by sublimation. Alizarin has 
also been obtained synthetically by several methods, but these 
are not necessary to record here. Pure alizarin forms fine 



ORGANIC PIGMENTS. 213 

orange-red crystals melting at 290°. It is almost insoluble 
in cold water and only slightly so in hot water, one litre 
dissolving 0*31 gr. of alizarin at 100°. It dissolves in sul- 
phuric acid with a red-brown colour, but on dilution the 
alizarin is precipitated in an unchanged state. When crystal- 
lised from moist ether, alizarin contains three molecules of 
water of crystallisation. If precipitated by acids from alkaline 
solutions, it also contains water, which is driven off at 100°. 
Alizarin behaves towards alkalies as a weak acid. It dissolves 
in caustic alkalies and in ammonia with a blue-violet colour, 
but is precipitated from such solutions by dilute acids. With 
calcium and barium salts, alizarin forms violet precipitates, 
and with all other bases it yields practically insoluble lakes. 
Those of alumina and tin are red, the others mostly of a 
darker colour. Towards these bases alizarin behaves as a 
strong acid, displacing even hydrochloric and nitric acids from 
their combinations. 

In commerce alizarin is always sold as a paste, which 
contains the hydrates of alizarin and the allied colouring 
matters in a fine state of division. The average quantity 
of dry colouring material in these pastes is about 20 per cent., 
but sometimes as much as 60 per cent, is met with. The 
two most important commercial shades are those known as 
alizarin blue shade (alizarin V) and alizarin yellow shade 
(alizarin G). The blue shade results when the sulphonation 
of the anthraquinone has not been carried beyond the mono- 
sulphonic acid stage. The yellow shade contains little true 
alizarin, but mostly anthrapurpurin and flavopurpurin. The 
latter body is responsible for the yellow shade, the former 
yielding a neutral red with alumina. 

Purpurin, Ci4H502(OH)3, which is found associated with 
alizarin in the madder root, crystallises with one molecule 
of water, and melts at 253°. 

Anthrapurpurin (isopurpurin) has the same empirical 



214 CHEMISTBY OF PIGMENTS. 

formula as the last-named body, merely differing from it by 
the orientation of the (OH) groups. It melts at 360°. 

Flavopurpurin is also isomeric with purpurin, and melts 
at above 330°. From the above brief descriptions of the 
properties of the colouring matters of the alizarin group, it 
will be easily understood how very numerous shades of lakes 
are produced from them, many of these differing greatly in 
tint, whilst being but slightly different in chemical composi- 
tion. Of the varieties of these lakes, the following are best 
known as commercial pigments : alizarin carmine, scarlet 
lake, burnt carmine, Indian lake, permanent crimson, per- 
manent violet, purple lake, sap green, olive green, olive lake, 
and others known under various fancy names. 

The chemical composition of these pigments cannot be 
regarded as regularly constant, but as far as possible this is 
indicated in the following paragraphs, in which a description 
of the chief well-defined compounds of this nature is given. 

Pure alizarin yields, as above mentioned, with calcium 
and barium salts a series of violet lakes, which vary slightly 
in tint according to the conditions under which they are 
formed. With tin and alumina it yields good red lakes, but 
with other bases the lakes are dark in colour. The slightest 
trace of iron salts suflSces to change the alumina red to a dull 
red or even to a brown colour. When the commercial alizarin 
is employed, the tint of the resulting lake necessarily depends 
on the exact composition of the alizarin. Ordinary alizarin 
red is the alumina lake of the yellow shade of alizarin, that 
is, it contains a large quantity of the trioxyanthraquinone 
lakes. Alizarin pink is prepared from the blue shade, and 
contains more of the true alizarin compound. They can all 
be obtained by dissolving the colouring matter in an alkali 
and precipitating the lake by a solution of alum. By varying 
the base or by using a mixture of tin and alumina, for example, 
different shades are obtained. According to recent researches 



ORGANIC PIGMENTS. 215 

of Liechti and Suida the composition of the normal alumina- 
lime ahzarin red lake is AlgOg, CaO, {C^iS^fi^)^, HgO. Traces 
of ferrous salts change the colour to a violet, and with ferric 
salts the darkening is very pronounced, a brown being often 
produced. A small quantity of chromium salt is suflScient to 
change the alumina red into a fine puce colour. 

In addition to the lakes of ahzarin and its oxy compounds, 
those of the sulphonated derivatives have a considerable 
importance. 

To prepare alizarin-sulphonic acid of the degree of sul- 
phonation required for general work, one part of alizarin is 
acted on by three parts of strong sulphuric acid containing, 
about 20 per cent, of free sulphuric anhydride, at 100° to 150°. 
The heating is continued until a sample dissolves completely 
in water. The reaction product is then dissolved in water 
and the excess of sulphuric acid is removed by treatment 
with barium or calcium hydroxide, and the filtered liquid is 
evaporated, when the necessary alizarin-monosulphonic acid 
is obtained. The free acid is soluble in water, and yields 
three series of salts. Those of the general formula C14H5O2 
(OH)2S03E are yellow or orange and are soluble in water. 
The sodium salt is the commercial product used for the 
preparation of many of the colours. The alkali salts of the 
general formula Ci4H502(OH) (OE) SO3E are of a red-violet 
colour, and those of the alkaline earths of a red-yellow colour. 
Those salts where the three available hydrogen atoms have 
been replaced, of the formula Ci4H502(OE)2S03E, are the 
most soluble, and are of an intense violet colour. 

The acid forms excellent lakes, as would be expected from 
its marked acidic properties, and the aluminium lake is of 
a deep carmine colour. It forms the basis of the most 
permanent of the crimson colours, and is known as " perma- 
nent crimson *' or '* alizarin carmine ". With tin salts as the 
base of the lake, orange shades are obtained. 



216 CHEMISTRY OF PIGMENTS. 

Fine colours belonging to the series of lakes can also be 
prepared by the ilse of nitro-alizarin. Two mononitro 
derivatives of alizarin are known, that termed the ^-variety- 
being the most generally employed. This is obtained by 
treating the blue shade of alizarin in a fine state of division 
with nitrous fumes. The purified nitro compound has the 
formula Ci4H502(OH)2(N02) and forms soluble red-coloured 
salts with the alkalies. With alumina it yields a fine insoluble 
orange, and with iron salts a red violet. 

An alizarin blue is known, but it has not been used to any 
great extent for pigment work. Several closely allied varieties 
are recognised, but even the best of them is not so fast to 
light as indigo, and is not fit to replace the latter. The 
alizarin blues are yielded by heating nitro-alizarin with gly- 
cerine and sulphuric acid, and appear to be quinoline-ahzarin 
compounds. Green colours are now used prepared from 
alizarin. These are those sold under the names : sap green, 
olive green and olive lake. Alizarin green is formed by 
treating alizarin blue with a large excess of fuming sulphuric 
acid, and subjecting the resulting product to the action of 
either alkalies or acids. The colour thus obtained is known 
as '* alizarin blue-green,'* and if it be heated to 130° with 
concentrated sulphuric acid alizarin green is formed, which, 
after separation and washing with water, forms fine blue-grey 
needles. As seen in commerce, however, it is a red-brown 
solution of the colour, which smells of sulphurous acid and 
when boiled gives a blue precipitate. This is used for dyeing 
purposes and is usually mordanted with potassium bichromate. 

For the detection of alizarin colours a spectroscopic exa- 
mination is most useful, as they all give more or less 
characteristic absorption bands which should be compared 
with those yielded by colours of known origin. The alizarin 
colours may be distinguished from madder colours by boiling 
them with a solution of aluminium sulphate. In the latter 



OEGANIC PIGMENTS. 217 

-case the solution is strongly fluorescent. Concentrated min- 
eral acids remove the base from the lake, and the free acid 
may then be examined. Bleaching powder destroys the 
•colour of most of the ahzarin compounds, but in some cases 
very slowly, especially in the case of the most permanent 
reds. None of them can, however, withstand the simultaneous 
action of an acid and chloride of lime. 

Campeachy Lakes. 

The Campeachy lakes, as they are usually called, are 
lakes prepared from logwood (HcBmatoocylon campechianum), a 
tree abounding in the West Indies, Mexico and, generally, 
in South America. When felled, the wood of the tree is 
nearly colourless, but it soon assumes a dark reddish-brown 
colour, which is deeper on the surface of the wood than in 
the interior. It is evident, therefore, that the colouring 
principle is the result of a chemical change after the felling 
■of the wood ; but whether this is merely an oxidation pro- 
cess, or is at the same time accompanied by the hydrolysis 
of a pre-existing gluQOside is not a matter of certainty. It 
appears most probable that the glucoside is in the first place 
^plit up into a sugar and haematoxylin, and that the latter 
is afterwards partially oxidised to haematin. An aqueous 
extract of the wood is a well-known commercial article, and 
whether used as a dye-stuff or for the precipitation of lakes, 
it is important that the evaporation of the water be conducted 
at as low a temperature as possible, and that oxidation be 
not allowed to proceed too far. The fermentation, as it is 
called, of the wood, by which the glucoside is decomposed 
with the formation of haematoxylin, takes place best when 
the wood is rasped into thin shavings and moistened. 

HcRmatoxylin, C^jIIj^Oe + SHgO, the initial active principle 
of logwood, crystallises in yellowish prisms having a sweet 
taste. It is very soluble in water and in alcohol, and also in 



218 CHEMISTRY OF PIGMENTS. 

alkalies. It can be obtained by treating the aqueous extract 
of logwood, or the powdered wood itself, with ether, and 
evaporating the liquid to a syrup, adding water and allowing 
it to stand for several days. The hsematoxylin, in a fair 
state of purity, is gradually deposited, containing three mole- 
cules of water of crystallisation if in the prismatic form, but 
only one if it occurs as fine granules. By heating to 100° a 
portion of the water is driven ofif, but a higher temperature 
is required to drive ofif all of it. Haematoxylin is not very 
soluble in cold water, but is easily so in hot water, alcohol, 
ether and carbon bisulphide. It contains several hydroxy! 
groups, and forms several well-defined methyl and acetyl 
derivatives (Monatshefte, xv., 139). It behaves as a weak 
acid, dissolving readily in solution of ammonia and caustic 
alkalies. These alkaline solutions are, when perfectly fresh, 
almost colourless, but they rapidly absorb oxygen from the 
air, with the formation of oxidation products, amongst which 
the most typical is haematin, and at the same time becoming 
bluish, then a deep red -brown. The more or less pure alka- 
line compounds can be prepared by "saljdng out " the alkaline 
solutions. Lead acetate gives with haematoxylin a bluish 
white precipitate, rapidly darkening on exposure to the air. . 
Tin salts produce a permanent rose-coloured precipitate 
sometimes used as a pigment. Ordinary alum gives a bright 
red colour, and aluminium acetate a fine purple ; there i& 
only a slight precipitation, however, unless other salts are 
present to assist. 

Hsematoxylin is very sensitive to alkalies and to acids,, 
being used as an indicator in chemical analysis. With free 
alkalies it yields a bluish colour, while with acids it is red. 
It is especially sensitive to ammonia and to calcium carbonate. 
Hence it is not to be regarded as a very permanent pigment,, 
so far as its initial shade is concerned. Chalk should never 
be used as a diluent. 



ORGANIC PIGMENTS. 219 

Hcematein, CigHigOe, is easily produced from hsematoxylin 
by atmospheric oxidation, especially in the presence of an 
alkali. It may be rapidly prepared by saturating an ammonia 
solution with haematoxylin, and allowing it to stand exposed 
to the air. fiaematein-ammonia, C6Hii(NH4)Oe, is formed^ 
from which acetic acid precipitates free haernatein. This 
body is a reddish-brown powder with a metallic lustre of a 
greenish hue. It is sparingly soluble in cold, but more easily 
so in boiling water. It is only slightly soluble in alcohol 
and acetic acid, and not very soluble in ether. Alkalies, 
however, dissolve it with avidity, the solution being at first 
blue or purple, but on oxidation by the air it darkens con- 
siderably, becoming of a deep brown colour. 

It forms a well-defined ammonium salt, which occurs as 
a deep violet powder consisting of microscopic prisms, which 
dissolve in water with a purple, and in alcohol with a red 
colour. At 100° the ammonia is volatilised, or even at 
ordinary temperatures in a vacuum over sulphuric acid. 
With copper sulphate its solution gives a violet-blue precipi- 
tate, and with stannous chloride a violet precipitate. It 
reduces silver nitrate. By reduction with sulphurous acid 
a portion at least of the body is converted into haematoxylin. 
A sulpho acid is obtained by treating it with cold concentrated 
sulphuric acid, and is precipitated as an orange-red crystal- 
line powd,er by adding acetic acid to the sulphuric acid 
solution. It has the formula CigHi^(S03H)0g. 

The reactions obtained from preparations of logwood 
are due to the simultaneous existence of haematoxylin and 
haematein. Dilute acids turn the colour yellow, but excess 
of strong acid gives a red colour. Sulphuretted hydrogen 
decolourises the solution, and sulphurous acid turns it yellow. 
Alkalies give at first a red, then a violet and finally a brown 
colour. Lime, barium and most of the heavy metals pro- 
duce characteristic precipitates. 



220 CHEMISTRY OF PIGMENTS. 

Stannous hydroxide gives a well-defined violet lake, 
whilst stannic salts behave as acids, turning the colour 
red. Salts of iron yield a blue-black colour, so deep that the 
iron compounds, of logwood are employed with great success 
as inks. Mercuric salts give an orange, antimony salts a 
carmine, and bismuth salts a violet precipitate. Alum gives 
at first a yellow colour, which becomes red after a time : 
while aluminate of sodium gives a blue-violet precipitate 
insoluble in excess of alkali. 

This reaction is said to be so delicate that logwood colour 
may by it be detected even when mixed with other colours. 
Another very well-defined test is the colour produced by 
bichromate of potassium. This test is best applied by boil- 
ing a piece of wool in a solution of potassium bichromate, 
and then immersing the wool in the colour decoction. In 
the presence of logwood it will be dyed an intense black. 

To isolate the colour principles the lake is acidulated and 
the acid aqueous liquid is shaken with amyl alcohol. The 
alcoholic liquid is then extracted by a solution of borax. To 
purify the colour, the borax solution is rendered acid and 
the colour again extracted with amyl alcohol, and the solvent 
evaporated. 

The best defined of the lakes of this important colour 
{which, however, find their chief employment in the dyeing 
industry) are the following : — 

Aluminium salts yield deep violet-grey shades, varying 
according to the exact method of treatment adopted in the 
manufacture. Ferrous salts give blue-black lakes of great 
intensity, whilst numerous varieties are produced by using a 
mixture of the two metals. With chromates, logwood de- 
coctions yield black colours which gradually turn green on 
exposure to light. By the use of potassium ferricyanide, etc., 
in dyeing operations, very fine and permanent deep blue shades 
oan be obtained. 



ORGANIC PIGMENTS. 221 

In the examination of the logwood lakes the following 
points are to be noted. If to the lake a few drops of concen- 
trated hydrochloric acid be added, the colour produced is a 
cherry red. A spot of this is absorbed by blotting paper ,^ 
and touched with a solution of aluminate of soda, which at 
once turns it blue. The blue and violet lakes leave on ignition 
an ash consisting of alumina or alumina and iron oxide,, 
or the base may consist almost entirely of oxide of tin. 
The black lakes leave an ash containing alumina with a large 
amount of iron oxide, or, more usually, chromium or copper 
oxide. Free chlorine (treatment with bleaching powder) 
readily bleaches all logwood colours. By boiling with glacial 
acetic acid, the colouring matter is dissolved, the acid having 
a rose-red colour, changing to yellow on heating. On adding 
ether and then sufficient water to cause the ether to separate, 
any indigo present will be found either in the ether or at the 
junction of the two layers, whilst the logwood will be present 
in the lower layer, colouring it a reddish-blue. If the colour 
is not very pronounced, a few drops of hydrochloric acid are 
added. The aqueous layer will then be a fine red colour. 

Quercitron Bark Lakes. 

Amongst the natural yellow colouring matters, all of 
which are of vegetable origin, the most important are the 
lakes prepared from the bark of Qtcerctcs tinctoria or *' black 
oak,'' which is found abundantly in the southern parts of 
the United States. The bark itself is a regular commercial 
article, usually appearing in the market as a mixture of fibres 
and coarse bufif or yellow powder. A more concentrated 
form of the colouring matter is that known under the name 
** flavin,'* which is a preparation obtained by treating the 
bark with sulphuric acid (somewhat analogous to garancin), 
and which contains a large proportion of the colouring principle 
of the bark, quercitrin, together with its decomposition pro- 



222 CHEMISTRY OF PIGMENTS. 

duct quercetin. ** Aurantine " and '* patent bark " are similar 
preparations. 

Quercitrin, the active colouring principle of the bark, is a 
glucoside, about the constitution of which much discussion 
has arisen. It may be prepared in a state of purity by treat- 
ing the coarsely powdered bark for six hours with 85 per 
cent, alcohol at boiling temperature. The alcohol is recovered 
from the extract, acetic acid is added, and a great deal of the 
extraneous matter is precipitated by the addition of an alco- 
holic solution of acetate of lead ; the excess of the latter re- 
agent is removed by sulphuretted hydrogen, and the filtered 
liquid is evaporated to dryness. The residue is dissolved in 
alcohol, and the filtered solution precipitated by the addition 
of water. The quercitrin is mostly thrown down by this, 
and is purified by recrystallisation from boiling water. 

Quercitrin crystallises from water or dilute alcohol in 
small yellow glancing needles or tablets. It is easily soluble 
in absolute alcohol, slightly so in cold water, but more so in 
hot water. It is nearly insoluble in ether. When anhydrous 
it melts at 169° and at higher temperatures is decomposed 
with the formation of — inter alia — quercetin. The air-dried 
preparation, containing possibly a molecule of water of 
crystallisation, melts at 173° to 176°. A solution of quercitrin 
is coloured an intense green by ferric chloride solutions. 

Its solutions are precipitated by lead acetate, but not 
when much free acetic acid is present. It easily reduces 
silver and gold salts in the cold. Quercitrin is easily dissolved 
in alkalies, the solution however soon becoming brown on 
exposure to the air. 

Liebermann has assigned to it the formula CggHggOgo, but 
the more modern researches of Herzig {Monatshefte f. Chem., 
xiv., 58) strongly support the formula C^iHggOig or probably 
CgjHgoOii + HaO. By the action of boiling dilute sulphuric 
acid the body, which is clearly a glucoside, splits up into 



OEGANIC PIGMENTS. 223 

quercetin and the sugar rhamnose. Assuming the formula 
to be CgiHgoOii, when anhydrous the reaction may be ex- 
pressed as follows : — 

CaHaoOji + 2H2O = C8H14O8 + G15H10O7, 

the products being hydrated rhamnose and quercetin. 

According to Wachs, the so-called quercitrin found in 
numerous other plants, such, for example, as Thuja and 
Sophora, is a compound of quercetin with one molecule of 
rhamnose and one of glucose, thus differing from normal 
quercitrin by containing an extra molecule of sugar. 

At all events no less than four well-defined glucosides 
which yield quercetin on hydrolysis have been described. 
These are (1) quercitrin, which yields on hydrolysis one 
molecule of rhamnose ; (2) rutin, which occurs in ordinary 
rue, and yields two molecules of rhamnose ; (3) Viola- 
quercitrin, which is extracted from the flowers of viola tricolor 
and yields dextrose on hydrolysis ; and (4) osyritin, from a 
Cape sumach, osyris compressa, which yields dextrose, but in 
different proportion to (3). 

Quercetin, the product of the hydrolysis of quercitrin, forms 
a yellowish-gold crystalline powder, which is insoluble in 
cold and only very slightly soluble in hot water. 

W. H. Perkin recommended the following method for the 
manufacture of quercetin. The bark in powder is washed 
with salt solution to remove impurities, and then extracted 
with cold dilute ammonia. The extract when neutralised with 
dilute sulphuric acid, deposits a brown amorphous precipitate 
containing little or no colouring matter ; this is filtered off, 
and the clear lemon-yellow solution which contains the 
glucoside quercitrin is acidified and boiled, when crystals 
of quercetin soon begin to separate. These are collected 
while the mixture is still warm, in order to prevent their 
contamination with a brown flocculent matter which after- 



224 



CHEMISTRY OF PIGMENTS. 



wards separates. The nearly pure quercetin can be com-^ 
pletely purified by recrystallisation from dilute alcohol. It 
is almost insoluble in ether. By rapid heating it melts 
at about 250°, or when anhydrous, according to Wachs, at 
299°. At higher temperatures it sublimes, part being decom^ 
posed and part un decomposed. The alcoholic solution gives 
an intense green with ferric chloride solution, the colour 
changing to dark red on warming. Acetate of lead gives a^ 
red precipitate. Silver and gold salts are easily reduced in 
the cold by it, and copper salts when boiled with it in solu- 
tion. Corresponding to Liebermann's old formula for quer- 
citrin, C24HigOii has been assigned to quercetin, but in the 
light of modern researches there appears no doubt that 
CigHjoOy is the correct formula. 

Quercetin has been obtained by Perkin and Pilgrim (Journ. 
Chem. Soc, 1898, 267) from the Indian dye-stuff asbarg- 
(Delphinium Zalil), but the nature of the glucoside with which 
it was probably in the first instance associated has not been 
determined. It also occurs to a small extent in the root of 
Podophyllum emodi (Dunstan and Henry, Journ. Chem, Soc, 1898,. 
209), and also in the leaves of New South Wales sumach 
(Rhu^ rhodanthema) , and in various other plants, such as the 
catechu-producing trees. 

The most probable constitution of quercetin, which is- 
supported by a great deal of experimental work, is 



H 
C 



O 



CH GOH 



OHC 



HC 




C 



C 




C C 



GOH 





COH 



CH CH 



COH CO 



Perkin {Journ, Chem. Soc, 1896, 1447) has shown that 



ORGANIC PIGMENTS. 225 

quercetin and its allies (such as fisetin, rhamnetin, etc.) form 
well-defined additive compounds with acids. This property 
may possibly be of use in enabling one to distinguish between 
this group of natural yellow colours and all other groups. 
For example, a saturated boiling solution of quercetin in 
acetic acid yields, on the addition of a few drops of sulphuric 
acid, a glistening mass of yellow hair-like needles. On 
separation and washing with acetic acid and drying at 100° 
they are decomposed quantitatively by water into sulphuric 
acid and quercetin. 

The lakes of these coloured principles are usually made 
with an aluminium basis, the precipitate being of a very 
beautiful yellow colour. No standard for the exact quality 
of such a lake can be laid down, but it is important to deter- 
mine that the ash does not consist of a neutral body that has 
been used as a diluent. 

If the compound be acidulated and the quercetin extracted 
with alcohol the solution. will give a green colour with ferric 
chloride ; if acidulated and treated with sodium amalgam it 
assumes a fine purple-red colour, and on concentration yields 
red prisms which dissolve in alcohol and a little free alkali 
with a green colour, the solution being rapidly reoxidised on 
exposure to the air. Some samples will allow of fairly pure 
quercetin being separated, which should then possess the pro- 
perties given above. On fusion with caustic alkali, quercetin 
yields protocatechuic acid and phloroglucinol, which may be 
searched for. 

Rhamnus Lakes. 

The berries of various species of Ehamnus, including the 
common buckthorn, B, cathartica, yield green and yellow 
colours of some importance in dyeing, calico printing, and 
artistic work. 

15 




226 



CHEMISTRY OF PIGMENTS. 



The following are used :- 



Name. 


Frait of. 


Description. 


Persian berries (from 


B. amygdalina 


j Size of a pea, greenish yellow. 


Aleppo and Smyrna) 


B. oleoides 


1 hard shrivelled surface, di- 




B. saxatiUs 


visible along well-marked 
! depressions into four parts, 
each containing a triangular 
seed, bitter taste. 


Avignon berries^graines 


B. inf ectoria 


Smaller than above, only two 


d*Avignon (French 


B. alatema 


seeds. 


berries) 






Spanish berries 
Italian berries 


B. saxatilis 
B. infectoria 


1 Very similar to French 
1 berries. 


Hungarian berries 


B. cathartica 



Others are obtained from the Morea^ Wallachia, and 
Bessarabia, but the real Persian berries are the most 
esteemed, and these especially when gathered in the unripe, 
yellowish-green condition, but not when they are pure 
yellow or brown to black. 

When an aqueous decoction of Persian berries is allowed 
to stand, surface moulds grow, the Uquid becomes ropy, and 
fermentation takes place, with the separation of a bright 
yellow insoluble powder. 

Gellatly, and later Schiitzenberger, showed that these 
berries contained the glucoside xanthorhamnin. Lieber- 
mann and Hormann showed that this, by boiling with dilute 
mineral acids, or by the action of the natural enzyme ^ 
of the berries, forms isodulcite and a colouring matter, 
rhamnetin. This latter was shown by Herzig to be a methyl 
derivative of quercetin (he believed it to be a dimethyl 
ether). Later he showed that quercetin was probably 

^ This enzyme rhamninase is precipitated by alcohol from the cold water 
extract of the fruit of B. infectoria as a pasty mass containing 28 to 50 per 
cent, of solid matter ; it is very soluble in water, and its activity does not 
diminish appreciably on keeping. The dry substance contains 17 per cent, 
mineral salts, 53 per cent, substances coagulated by heat, and galactan. A 
temperature of 70° is most favourable to its action, which is destroyed at 85^ 
(0. and G. Tanret, Btdl, Soc. Chim,, 1899, iii., 21, 1073-75). 



ORGANIC PIGMENTS. 227 

C15H10O7, and rhamnetin probably CigHigOy (= C^^KgO^GK^). 
Lefort, and later Schiitzenberger, showed that xanthorhamnin 
was not a chemical individual, and the latter chemist 
extracted two glucosides, a - rhamnegin (xanthorhamnin), 
yielding rhamnetin, and ^-rhamnegin, yielding a colour more 
soluble in alcohol and acetic acid. Herzig extracted a gluco- 
side yielding a colouring matter, the acetate of which melted 
at 169° to 171°, whereas acetyl-rhamnetin melts at 183° to 185°. 
This he separated by alcohol into rhamnetin and quercetin, 
and considered the glucoside to be a loose compound of 
xanthorhamnin and a glucoside of quercetin, which he 
named rhamnin. 

Later, A. G. Perkin {Joum. Ghem, Soc, 1895,496), who has 
done so much good work on natural colours, with J. Geldard 
took up the examination of Persian berries, and, allowing the 
or^inge-brown liquid obtained by soaking the ground berries 
(in a calico bag) with ten times their bulk of water to ferment, 
obtained a yellow powder, separated by the action of the enzyme, 
as was well known. When this precipitate no longer increased 
in quantity and had settled, the clear liquid was removed 
and the precipitate dried at 100°, and digested with boiling 
toluene. This gave a crop of brown needles agreeing fairly 
in composition with C17H14O7, and melting at 214° to 215° — 
identical with rhamnazin prepared by these authors from a 
purchased rhamnus colour, " rhamnetine ". The residue from 
the toluene extraction was crystallised from a large bulk of 
alcohol, and gave, on recrystallisation in alcohol' and acetic 
acid, rhamnetin, G^^^Jd^, M.P. above 280°, and sparingly 
soluble. The alcoholic mother liquors and aqueous main 
filtrate gave, on further treatment, minute yellow needles, 
readily soluble in alcohol and acetic acid, and crystallisable 
from ether and chloroform, agreeing in composition with 
quercetin, C15H10O7, and yielding the characteristic acetyl 
derivative colourless needles, M.P. 189° to 191°. 



228 CHEMISTRY OF PIGMENTS. 

The authors, in summing up, state : — 

** These results are interesting, and show that xantho- 
rhamnin, together with the unknown glucoside of rhamnazin, 
are readily decomposed at 40° by the ferment present in the 
berries. This, on the other hand, exerts but little influence 
on the glucoside of quercetin (quercitrin ?), which is also 
present. 

"The colouring matters obtainable from Persian berries are 
therefore rhamnetin, or quercetin monomethyl ether ^ CigH^gOj, 
rhamnazin or quercetin dimethyl ether, CijU^fij, and quercetin, 
C15H10O7, itself." 

They are of opinion that Schutzenberger*s /3 rhamnetin 
was quercetin. 

Xanthorhamnin is prepared (Liebermann and Hormann) by 
boiling for eight to ten hours powdered berries with three 
times their weight of 85 per cent, alcohol. On allowing to 
cool and stand for twenty-four hours a large quantity of 
impure glucoside, with a little free colouring matter, is 
deposited as a resinous mass. The clear solution allowed 
to stand for some days in a cold place deposits pure xan- 
thorhamnin in pale yellow cauliflower-heads, and in such 
quantity as to render the liquid pasty. The total yield is 
about 12 to 13 per cent. By recrystallisation several times 
from alcohol, and then from alcohol with water and ether, 
it may be obtained in distinct crystalline needles. It does 
not crystallise from an aqueous solution. It is soluble in 
water and alcohol, but not in ether, benzene or chloroform. 
It should be dried rapidly over H.^S04 i^ * vacuum, but not 
by heat, as it melts at a low temperature when moist, but 
above 130° (it contains 2 molecules alcohol, which it loses 
at this temperature) when dry. The above authorities 
assigned the formula G^^^Jd^i^ to xanthorhamnin. Both 
Fehling's solution and ammoniacal silver nitrate are reduced 
by it. 



ORGANIC PIGMENTS. 229 

Normal lead acetate turns a solution orange, but the 
addition of ammonia precipitates an orange-coloured lake. 
Alcoholic KOH causes the separation from the alcohoUc 
solution of a potassium derivative, C4gHg2029K4. It is stated 
by Schiitzenberger that twelve acetyl groups can be intro- 
duced on acetylation ; fusion with caustic potash causes 
formation of phloroglucin and protocatechuic acid, with an 
acid body giving an intense red colour with the alkali. 
Sodium amalgam causes the production of the former bodies, 
but not of the coloured body. 

Mineral acids eiOfect the hydrolysis of xanthorhamnin, but 
acetic acid does not, though the glacial acid be used. 

The mixture of colouring matters known formerly as 
rhamnetin, the nature of which was indicated by Perkin 
and Geldard, is readily soluble in fixed alkalies, less readily 
in ammonia, and only slightly in alkaline carbonates. Its 
alcoholic solutions give a yellow precipitate with tin and 
alum solutions, a reddish brown with copper acetate, and 
an orange with lead acetate. 

The behaviour of quercetin, rhamnetin and rhamnazin 
to acids is characteristic. 

Quercetin easily forms a sulphate, hydrobromide, hydro- 
chloride and hydriodide by addition of the ax;id to a boiling 
aqueous solution. 

Bhamnetin forms a sulphate with difficulty, and no halides. 

Bhamnazin requires a still greater excess of sulphuric acid- 
to form an unstable sulphate, and forms no halides. 

Those compounds are decomposed by water, and must be 
washed with acetic acid to free them from excess of mineral 
acid. In the case of the sulphates this must be done 
quickly. 

This property of forming salts is, as previously mentioned, 
valuable in characterising the members of the quercetin group 
from one another and from other substances. 



230 



CHEMISTRY OF PIGMENTS. 



Adopting the quinonoid formula previously given for 
quercetin :^- 



O 



OH 



OH 



OH 


CO 


OH 


/ \0H 






rhamnetin becomes 






OH 




OH /\/\ 


/ 


\ 

\ 






OH CO 


\ 


/ 




OCH, 





OH 



while in rhamnazin a further hydroxy group is replaced by 
the methoxy group ; the addition of this group enfeebling 
the acid-combining power of the pigment. 

Bhamnose (isodulcite), CH3(CH, 0H)4CH0 + H2O. The 
sugar of xanthorhamnin melts at 93° when anhydrous, and 
at 122° to 126° when crystallised from acetone, and is also 
l8Bvorotatory ; whereas the modification has ap = + 10°, and 
the 7 variety obtained by warming this to 90° has a© = + 20°, 
which after keeping goes back to + 10°. 

Persian berries are used principally in calico printing. 

A steam yellow is obtained by the addition of alum to the 
aqueous extract, thickening the lake with gum acacia and 
adding stannous hydroxide. 

Steam orange is obtained by the use of stannous chloride 
and sodium acetate (equivalent of stannous acetate) as a 
mordant or lake base. 

Steam green is prepared by the use of stannous chloride 
and alum with acetic acid and potassium ferrocyanide, and sul- 
phuric or oxalic acid, gum being added to thicken (? should some 
iron salt be added to form Prussian blue and thus a green). 



ORGANIC PIGMENTS. 231 

Persian berry carmine is a brown or yellow tin lake. 

The colours known as brown pink and stU de grain are 
lakes produced from these berries. 

These colours, generally speaking, are less fast and more 
expensive than those obtained from quercitron. 

Sap Green. — The pigment known as sap green, used to 
some extent by artists, as are the Persian berry lakes, is 
prepared by fermenting the decoction of buckthorn berries 
(B, catharticus)y lime water and gum acacia being added. After 
a week, alum is also added to the liquid strained from the 
berries, and the mixture concentrated by evaporation and the 
residue hung up in a pig's bladder to dry. This green buck- 
thorn lake is mentioned by De Mayerne (1573-1656), a friend 
of Eubens. 

A similar but poorer green is prepared from the black 
alder {B. frangula) and the evergreen privet. 

An alizarin lake is also employed under the name of ** sap 
green " {vide supra). 

Lokao, Chinese green, is said to be prepared from the 
twigs of certain species of rhamnus (B, chlorophorus (globorus) 
and B. utilis) by boiling the bark with water and immersing 
cotton cloths, which take up a colourless substance, this turn- 
ing green on exposure to air. The process is repeated until 
a quantity of colour has accumulated. It is then washed 
with cold water and boiled with water in which cotton yarn 
is laid. This takes up the colour, which is washed off and 
collected on paper. 

Charoin of Lyons prepared a green from rhamnus bark by 
boiling it with water and adding Hme water : on exposure to 
air in shallow vessels a green precipitate formed, which was 
increased by the addition of potassium carbonate. This 
seems more plausible than the reported method of the Chinese, 
and the product would appear to be a lake. 

These greens, though of a rich colour, have not a good 
reputation for permanence. 



232 CHEMISTRY OF PIGMENTS. 

The sap-green of a well-known firm of artists' colourmen 
was a chlorophyll-like looking colour, but as on ignition it 
left a blue ash discoloured by hydrochloric acid and contain- 
ing about 36 per cent, silica, it was probably gamboge and 
ultramarine, a more permanent colour than real sap-green. 
This was an oil colour. Sap-green is usually used in water. 

Brazil Wood Lakes. 

Brazil wood is the product of CoRsalpinia Brasiliensis, a 
tree growing in the forests of Brazil. The red -dye woods 
known in this country under the names Sapan wood, Lima 
wood, Bahia wood, etc., are all products of various closely 
related trees of the same natural order, and take their names, 
as is evident, from the port of exportation. They all yield 
similar colours, but that from Brazil wood is the one which 
has been fairly thoroughly investigated, and whose chemistry 
is best understood. The colouring matter appears to be 
present in the form of a glucoside, which is probably identical 
in all the woods above named. It is decomposed by the 
action of a ferment in the presence of water, or by boiling 
with dilute acids, into glucose and the colouring matter, 
brazilin. This body is colourless itself, and appears to be 
closely related to haematoxylin, from which it differs in 
composition by only one atom of oxygen. 

Brazilin forms white, shining needles of the formula 
CigHj^Og, and contains the equivalent of one and a half 
molecules of water of crystallisation. It is soluble in water, 
alcohol and ether : its solution on exposure to the air, espe- 
cially in the presence of alkalies, is rapidly converted into 
a bright red fluid, from which acids precipitate the analogue 
of haematein, namely brazilein. 

Brazilein, CigHigOg, forms minute crystals of a greyish 
lustre, containing one molecule of water of crystallisation. 
It is formed from brazilin by several methods, such as the 



OEQANIC PIGMENTS. 233 

interaction of the latter body with iodine, or by treating 
brazilin in acetic acid with potassium nitrite. A careful 
comparison of the brasileins prepared by the various methods 
has proved conclusively that they are all identical {Berichte, 
23, 1428). 

When powdered, brazilein is of a reddish-brown colour, 
and dissolves only slightly in cold, but more readily in hot 
water; the solution is of a yellowish-pink colour with a 
greenish-orange fluorescence. On the addition of an alkali 
the solution becomes crimson red, ultimately turning brown 
on exposure to the air. 

Kopp has proposed the formula CggHigOy for brazilin, but 
the researches of Schall and Herzig have conclusively proved 
that the previously quoted formula is correct. A large num- 
ber of bromine and alkyl derivatives have been prepared 
and described which all support that formula, for details of 
which the original papers must be consulted (see Berichte , 
23, 1428 ; 21, 3009 ; 27, 524 ; Monatshefte, 15, 139 ; 14, 56). 

The exact shade of the lakes formed from the extract of 
Brazil wood, in which form the colour is usually found, 
depends on the relative quantities of brazilin and brazilein 
present. Brazilein gives a good red lake with alumina, a 
greyish-violet to black with salts of iron, and browns with 
mixtures of the two. Stannic chloride gives a red, and there 
is also a lake of a fine dark crimson colour formed by the 
action of potassium bichromate. This appears to be due to 
the action of the chromic acid on the brazilin and brazilein, 
with a partial reduction to a lower oxide of chromium, 
which is of a basic character, and unites with the brazilein. 
Lead salts give a dirty blue lake. One of the most success- 
ful methods of obtaining these lakes is to pass a current of 
air through a solution of brazilin containing the requisite 
metallic salt, also in solution. 

Brazilein and its derivatives can be reconverted into 



234 CHEMISTRY OF PIGMENTS. 

brazilin and its derivatives by reduction by means of zinc 
dust. 

If these lakes are pure, the residue left on ignition will be 
found to consist almost entirely of the metallic oxide with 
which the brazilein is combined. Sometimes starch or chalk 
will be found used as a diluent, but the use of the lakes is too 
small to cause much adulteration to be practised. Strong 
hydrochloric acid turns these lakes a pink colour, which is 
materially altered on dilution with water. Hypochlorous 
acid or chlorine rapidly bleaches them. 

Alkanet Lakes. 

Alkanet, as known in commerce, is the root — or portions 
of the root — of Anchusa tinctoria. It contains a red colouring 
matter of an acid nature which may be prepared by boiling 
the root with water in order to remove all soluble matter, 
drying it, and exhausting with alcohol.' The alcoholic solution 
has a violet colour and is slightly acidified with hydrochloric 
acid, and evaporated to dryness. The dry residue is treated 
with ether, and this, on evaporation, leaves the red colouring 
matter in an impure condition as a dark red resinous mass. 

This colouring matter was described so long ago as 1814 
by Pelletier, who regarded it as a kind of fatty acid, and gave 
to it itis name — anchusic acid. The formula assigned to it 
(old notation) was CggHgoOg. The same body appears to 
have been described by John (Chemische Schriften, iv., 85) 
under the name pseudo-alkannin, which he stated was 
present in the root to the extent of 6*6 per cent. The more 
recent investigations of Carnelutti and Nasisi (Berichte, 13,. 
1514) are the basis of our present knowledge of the active 
principle of the root. In preparing the acid, they exhausted 
the commercial extract of the root with a solution of potash, 
and from the alkaline solution they obtained an impurity 
present by shaking with ether. The potash solution de- 



ORGANIC PIGMENTS. 235 

posits the alkannin, as it is now called, on being saturated 
with carbonic acid. It forms a dark red mass soluble in 
chloroform and acetic acid, but only sparingly so in other 
organic solvents. The formula assigned to the acid was 
C15H14O4. A crystalline diacetyl compound was obtained by 
treating the acid with acetic anhydride and sodium acetate. 
A barium salt containing two atoms of barium to three mole- 
cules of alkannin was obtained by precipitating an alcoholic 
solution with ammoniacal solution of barium chloride. 

Alkannin appears to be related to the red colouring matter 
of Sanders wood. Liebermann and Eomer {Berichte^ 20, 2428) 
investigated the compound in 1887, and after a series of 
analyses they came to the conclusion that the formula of 
the acid was either that proposed by the above-mentioned 
chemists, or C15H12O4. They consider that alkannin is a 
methylanthracene derivative, probably its dihydroquinone or 
its dihydride. 

The alcoholic solution of alkannin is of a crimson colour, 
and is permanent to light and heat. It gives a blue colour 
with alkalies, and a blue-violet precipitate with aluminium 
salts, the acetate being the best to use for the preparation of 
the lake ; a crimson precipitate with stannous chloride, and a 
purple precipitate with stannic chloride. Lead acetate gives 
blue, and iron salts violet, precipitates. 

According to Allen, the best test for alkannin is an 
examination of its absorption -spectrum. Its solution in amyl 
alcohol gives the best results, and exhibits three equidistant 
bands in the blue-green part of the spectrum. On adding 
ammonia to this solution, these bands give place to two fresh 
bands, one nearly coincident with, and the other on the red 
side of the D line. Bujard and Khnger {Zeit. ang, Chem., 1890, 
26) state that the alcoholic solution acidified with acetic acid 
gives a well-defined absorption spectrum, the three character- 
istic bands being as foUows : the first is near and on the more 



236 CHEMISTRY OF PIGMENTS. 

refrangible side of the D line ; the second commences at E 
and extends to beyond b ; and the third, which is faint, is 
close to F. On rendering the solution alkaline the blue 
solution shows two bands, one of which is midway between 
C and D, and the other commences at about D. 

Alkannin resembles orchil (archil), but differs from the 
colouring matter of logwood, Brazil wood, etc., by being 
extracted from its ammoniacal solution by ether. 

When natural madder lakes were articles of general 
commerce, adulteration of the latter with alkanet lakes was 
sometimes practised. A reaction said to be characteristic of 
alkanet lakes, and which was used to detect the presence of 
these bodies, was as follows : The lake was dissolved in 
acetic acid and the acetic solution was extracted with carbon 
disulphide; if alkannin were present the carbon disulphide 
solution was coloured an intense violet-red (see p. 210). 

Santal-wood Lakes. 

The wood of the so-called red sandal, Pterocarpus 
Santalinus, must not be confounded with that of the yellow 
sandal wood, Santalum album, from which the santal wood 
oil of pharmacy is distilled. Eed sanders wood, as it is 
more frequently called, together with the woods of the 
allied trees which yield the so-called barwood, camwood 
and caliatour wood, are used for certain tinctorial purposes, 
but to-day the lakes from these woods are almost entirely 
superseded by coal-tar colours. They all appear to contain 
a colouring matter of the formula G^^^fi^, and it is probable 
that this is identical in all the woods. It is termed santalin. 
It appears to be an acid, but its chemistry is not well 
understood. 

With stannous chloride the tinctures of the woods, espe- 
cially those of santal and barwood, yield blood-red lakes, and 



ORGANIC PIGMENTS. 237 

with ferrous salts a violet lake. A dark cherry-red lake is 
yielded by the use of tartar emetic. 

Archil Lakes. 

These lakes are now practically never used, as the coal- 
tar colours have superseded them, but the colouring matter 
is still used for other purposes, and a few lines treating of 
their general properties will not be out of place. Archil 
is the product of several species of lichens, of which the 
two principal are Bocella ficciformis and B, tinctoria. It 
comes into commerce as a paste or as a liquid. It is usually 
prepared by treating the finely chopped " weeds '* with dilute 
ammonia, keeping the mixture at about 20° till a dark violet 
paste has been formed. This paste, when diluted with am- 
monia and filtered, yields *'blue archil," and this, on gently 
heating to drive oJ0f the ammonia, yields the " red archil ". 

The pigment known as French purple is a lake obtained 
by treating the ammoniacal liquid with calcium chloride. 

The pasty archil consists chiefly of ammonia combined 
with a colouring matter called orcein. This body owes its 
origin to the action of air and ammonia on the orcin present, 
in the same way as haematein is formed from haematoxylin. 
The lichens contain a considerable quantity of complex 
ethers, from the decomposition of which orcin results. The 
principal of these are the following : — 

Erythrin (Erythric acid), C20H22O10. This body when 
boiled with alkalies yields orcellinic acid and picroerythrin, 
the latter body being decomposed by further treatment into 
orcinol and erythrol, with the evolution of carbon dioxide. 
These reactions establish the constitution of erythrin as the 
diorcellinic ether of erythrol. Orcellinic acid is a dihydroxy- 
toluic acid, whilst erythrol is a tetratomic alcohol closely 
related to the sugars. The relationships of these bodies are 
shown in the following table : — 



Diorcellinic arcid . 



238 CHEMISTRY OF PIGMENTS. 

Orcinol . . . C8H2(CH3)(OH)2H (methyl resorcinol). 

Orcellinic acid . . CbH2(CH3)(OH)2CO,OH 

O.C6H2(CH3)(OH)CO,OH 
GO.C6H2(CH3)(OH)2 

Erythrin . . . c,h/ f^^^^^^)^<^^«)^«^i 

\(0H)2 

Picroerythrin . '. c,^/ O0OmU0K,)0,K, 

\(0H)3 
Erythrol . . . C4He(OH)4 

The special characters of these bodies are without interest for 
our present purpose. 

Orcinol (Orcin) is a methyl-resorcinol, and therefore has the 
characters of a diatomic phenol. It occurs in the free state 
in several of the lichens used in the preparation of archil, 
but is chiefly a decomposition product of the above-described 
complex ethers which are present to so large an extent in the 
plants. It is a crystalline body melting at 68°, and on treat- 
ment with ammonia in the presence of atmospheric oxygen 
it yields the colouring matter orcein. According to Lieber- 
mann two compounds are formed, according to the conditions 
of the reaction. He states that if ammonia be in excess 
a body of the formula Ci^HigNgOg results, whilst if the reverse 
be the case the compound has the formula Ci^H^iNOg. 

The researches of Zulkowski and Peters (Monatshefte, 
11, 227-245), however, have shown that the previous formulae 
of these colouring matters are incorrect, and were based on 
the analysis of impure specimens. By careful procedure 
they obtained three distinct colouring matters from orcinol 
by the action of air and ammonia. They dissolved 60 
grams of ordnol in 200 c.c. of water and added 200 c.c. of 
strong solution of ammonia. After standing for two months 
the mixture was examined and after a series of separations 
the orcein was obtained in the crystalline condition. It 



ORGANIC PIGMENTS. 239 

forms a brown crystalline powder, of the formula C28H24N2O7, 
insoluble in water, but soluble in acetone, acetic acid, and 
alcohol. 

French purple, as above stated, is a calcium lake of 
orcein, but finds very little employment now. If an archil 
lake be treated with hydrochloric acid and shaken with 
€ther no trace of colouring matter will be dissolved, if 
the lake be made from pure archil. According to Slater, 
the presence of most other vegetable colours may be 
detected by treating 3 or 4 grams of the sample with 
100 c.c. of water and 50 drops of a solution of stannous 
chloride. On boiling the liquid a yellowish colour will 
remain if the archil be pure, but if logwood be present 
a bluish colour will persist, and if most other red woods 
are present the colour will be reddish. 

The colouring matter known as cudbear, or on the Con- 
tinent as perseo, is obtained by the action of ammonia or 
urine on various lichens, such as Lecanoria tinctoria and 
Variolaria orciruiy and is, therefore, very similar to orchil 
in its properties. The colouring matter of this substance 
appears to be either identical, or very closely related to 
that of archil, but sometimes the extract is considerably 
richer than that of the rocella lichens. Hence, it is fre- 
quently mixed with a considerable amount of mineral matter, 
usually common salt, not so much as a wilful adulteration as 
to bring the richer varieties down to one uniform standard. 

III.— COAL-TAR LAKES. 

The lakes produced from coal-tar colours have been 
indicated when dealing with the madder lakes, but in the 
present section it is proposed to deal with the lakes of the 
artificial colours at some length, as they have now assumed 
an importance which has gradually increased, with the 



240 CHEMISTRY OF PIGMENTS. 

increase in our knowledge of the now universally employed 
coal-tar colours. 

The natural colour lakes may, in general, be regarded 
as compounds of one or more natural colour acids with 
inorganic bases, with, at times, more or less mechanical 
admixture of excess of base or acid. Theoretically, however, 
the lake may be regarded as the true compound in the sense 
described. 

In the same way the lakes of the artificial colours 
must be regarded as true chemical compounds, although the 
mechanical admixture plays an important part in the pre- 
paration of the colours in actual practice. 

For the purposes of the present chapter, artificial colouring 
matters capable of forming lakes may be divided into three 
groups. These are as follows : (1) The artificial colour base s- 
containing nitrogen in combination with hydrogen, so that 
the base behaves as an ammonia derivative. (2) Artificial 
colours of a purely acid nature, capable of combining with 
an inorganic base. (3) Artificial colours in which both acid 
and basic functions exist simultaneously in a well-defined 
degree. Such bodies may be typified by a sulpho acid of an 
amido compound. 

In this sense then we understand a true lake, and it is 
necessary to here draw attention to the somewhat free use of 
the word ** base " in connection with this subject. As we 
are employing the word, it refers to a compound or an oxide 
of a metal capable of uniting to form a definite compound 
with an acid. The word is also employed (" lake base,'* etc.) 
when referring to a neutral body, such as sulphate of barium 
or china clay, which is employed as an absorbent, or as a 
diluent for a colour, but in the present work the word will 
not be employed in that sense. 

At the same time it must be admitted that the principles- 
of lake formation are not altogether as well understood as one 



ORGANIC PIGMENTS. 241 

could wish. Although we have emphasised the importance 

of recognising the principle of true chemical combination as 

the basis of the formation of lakes, there is considerable room 

for speculation as to the degree to which this combination 

is carried in a great number of cases which must be regarded 

as belonging to the class of true lakes. It is quite certain 

that advantageous precipitations of colour bases take place, 

when only a small proportion of the calculated molecular 

equivalent of the precipitating acid is used. This is especially 

the case when tannic acid is employed. Here, then, we have 

a case in which, whilst there is certainly a true chemical 

combination of the base and the acid, there exists in the 

compound far more base than the theoretical combination 

would require. It is usual to use the expression *' mechanical 

combination '* in such cases, and to escape from the difficulty 

of a lame explanation by the use of a term which is even 

more difficult to define than the original problem is to 

explain. In certain cases, where a voluminous precipitate, 

such as that of alumina in the hydrated state, is thrown 

down, a species of '' mechanical combination " is not difficult 

to assume. For example, when one adds a solution of 

ammonia to a solution of alum mixed with a salt of calcium, 

a voluminous precipitate is thrown down. It is of such a 

bulky, gelatinous nature that together with the mass of 

water which assists to make up the ** jelly," there is a 

considerable amount of lime salts : it is next to impossible 

to completely remove these lime salts by ordinary washing 

with water, and when the alumina is filtered off and dried, 

it will be found that there still remains an appreciable 

amount of lime in a state of intimate admixture with the 

alumina. But the quantity is not sufficient to explain the 

almost complete precipitation of a considerable excess of base 

by a small quantity of the precipitating acid, as in the case 

we have above quoted. 

16 



242 CHEMISTBY OF PIGMENTS. ' 

From a prolonged experience of compounds of the inor- 
ganic elements, which are more easily manipulated than the 
organic compounds from this point of view, we are acquainted 
with well-defined basic compounds, i.e., compounds of a base 
^vith an acid which are not of normal constitution, but 
contain definite molecular proportions of the base in excess 
of that required for the normal compound. In our present 
imperfect state of knowledge concerning the exact nature 
of the combination existing between many organic com- 
pounds, it appears to us that the most feasible explanation 
of the somewhat erratic combinations of these lake bodies 
is the existence of an analogous series of compounds to those 
which, as just mentioned, are well recognised between 
inorganic elements. This, however, is merely a matter of 
speculation, and need not, therefore, be further discussed 
here. We now pass on to the consideration of the coal- 
tar lakes, and in doing this we have arranged the lakes 
in groups according to their colours, without taking their 
chemical constitution into consideration, a practice which, 
as evident in the earlier chapters, would not have been 
convenient when dealing with the pigments of inorganic 
origin. 

Red Lakes. 

By careful manipulation practically any shade of red can 
be obtained from various coal-tar derivatives. The method 
of working will modify the shade to a very great extent, 
in spite of the fact that the constitution of the resulting 
colour will be practically unaltered. Hence, an accurate 
knowledge of the working details of lake manufacturing is 
indispensable to the manufacturer of this series of bodies, as 
the processes are not merely those of '* mixing ". 

The principal colouring matters which are employed for 



OEGANIC PIGMENTS. 243 

the preparation of the red lakes are members of the following 
groups : — 

1. The rosaniline group, or derivatives of triphenyl- 
methane, CH (0^115)3. 

2. The rhodamine group, or derivatives of amido-phenol- 
phthaleins. 

3. Azines, including the safranines, and the eurhodines. 

4. The sulphonated azo compounds, typified by crocein 
scarlet. 

5. The eosins, or halogen substituted phenol-phthaleins. 

6. The alizarin group. 

1. The Bosaniline Group. — The principal member of this 
group of colours, magenta, is that which is chiefly employed 
in the manufacture of lakes. Commercial magenta is in 
reality a mixture of the two coloura, rosaniline and pararos- 
anihne. The two bodies are, however, so nearly identical that 
wdth the exception of briefly indicating the difference in their 
constitution there is no need to further differentiate between 
them. 

The parent substance of the group is the hydrocarbon 
triphenyl-methane, CH (CqH^)^ ; the basic properties of the 
colours derived from this hydrocarbon being derived from 
amido groups introduced into the phenyl radical. Rosaniline 
is the triamido derivative of triphenyl-carbinol, of the con- 
stitution C(OH)(C6H4NH2)3, and differs only from para- 
rosaniline in the fact that the latter is the corresponding 
derivative of tolyl-diphenyl-carbinol, of the constitution 
C(OH)(C6H3 . CH3 . NH2)(C6H4NH2)2. The colour (consisting 
of a mixture of the two bodies) is manufactured by the 
oxidation of ordinary aniline by either arsenic acid, mercuric 
nitrate, or nitrobenzene. The bases are, when pure, quite 
colourless, but they form salts (with the elimination of 
water) with acids, which are the real colours employed. 

The usual form in which magenta is seen in commerce is 



244 CHEMISTBY OF PIGMENTS. 

as the hydrochloride, the rosaniline salt having the composi- 
tion CaoHigNgHCl, water being eliminated in the formation 
.of the salt. It is then in the form of rhombic crystals 
which have a metallic green colour in reflected light. The 
solutions are crimson, and are not fluorescent. It is not very 
soluble in pure water, but is readily so in acidified water and 
in alcohol. Caustic alkalies. separate the colourless base in the 
free state. Reducing agents, such as sulphurous acid, or zinc 
and acetic acid, decolourise solutions of magenta, eliminating 
the oxygen atom, with the formation of salts of leucaniline. 
After reduction in this way the solution is not re-oxidised by 
the action of the air (this distinguishes this colour from the 
somewhat similar colours, Magdala red and the safranines). 
Chloride of lime decolourises solutions of magenta. 

Sometimes the acetate is found in commerce. It has the 
advantage of being the most soluble of the rosaniline salts. 
Magenta is a colour which should, when pure, consist only of 
the two colouring matters mentioned. Impurities modify the 
shade, and this is reproduced in the lake which is prepared 
from it. It is sold under numerous names, amongst which 
are the following : Magenta, azaleine, roseine, fuchsine, 
rubine, etc. Magenta-violet is a frequently occurring colour, 
and consists of a mixture of magenta and mauvanihne ; the 
lakes prepared from this colour are of a much more violet 
shade than those from the pur^ colour. Cerise is an im- 
pure magenta salted out from the mother liquors after the 
preparation of the pure magenta. It contains a certain 
amount of a colouring matter called phosphine. Cardinal 
and amaranth are also mixtures of magenta and various 
impurities. 

Isorubin, or *' new magenta,'' as it is called, is the 
corresponding hydrochloride of triamido - tritolylcarbinol, 
C(0H)(CeH3. CHg. NH2)8. It is a colour of recent intro- 
duction, formed by the condensation of formaldehyde and 



ORGANIC PIGMENTS. 245 

orthotoluidine. It resembles ordinary magenta in appearance 
and properties, but gives colours of a bluer shade, and is 
more soluble in water. 

Maroon and grenadin are also more or less impure 
magenta. 

Many of the lakes in which magenta is the chief ingredient 
are compound lakes manufactured from magenta mixed with 
one or more other colours, such as various scarlets or cherry 
reds. Amongst the best lakes of magenta are those prepared 
with arsenious or resinic acid (the latter being a mixture of 
various resin acids). The colour of these lakes is very bright, 
but the arsenious acid compound is somewhat fugitive. The 
tannic acid lakes are also fugitive, and somewhat dull. A 
lake prepared with antimony salts and tannic acid is very 
permanent, but not as bright as the arsenious acid lake. 
The tannic acid lakes have the property of being soluble 
in alcohol. 

Magenta lakes, when undiluted, leave no ash, as they 
consist of organic bases in combination with volatile acids. 
Any ash present should be examined, ttnd may be regarded 
as a diluent either added to lighten the shade, or as an 
adulterant for the purpose of cheapening the colour. 

The colour should be entirely removed by treatment with 
sulphurous acid or by chloride of lime. In the former case 
exposure to the air does not restore the colour as it will do 
in the case of Magdala red and the safranines. If the lake 
be treated with a strong solution of caustic alkali, the free 
base may be dissolved out by ether. The colourless ethereal 
solution will dye silk a fine crimson, combination taking 
place between the base and some constituent of the fibre : 
or it will yield a fine crimson colour with a trace of acetic 
acid. 

For a full recognition of the constituents of a compound 
lake prepared from several coal-tar colours, special works on 



246 CHEMISTRY OF PIGMENTS. 

the analysis of this group of colours must be consulted. The 
enormous number of them, however, many of which are of 
almost identical properties, renders the task a matter of 
practical impossibility, unless the mixture is one of compara- 
tive simplicity. 

A colour known as acid magenta, magenta S,or rubine S, 
is sometimes employed for lake manufacture. It is a trisul- 
phonic acid of magenta, and forms lakes with bases instead 
of acids. Its colouring power is not so good as the basic 
colour, but it is very useful in combining with certain yellows 
for mixed shades. It is known also as acid fuchsine, and in 
an impure form as maroon S, grenat S, acid cerise, cardinal 
S, acid maroon, etc. 

2. The Bhodamine Group, — When phenols are heated 
with phthalic anhydride, a combination takes place accord- 
ing to the following reaction : — 

.COv C = (CeH,0H)2 

CeH,/ ^0 + 2CeH,. OH = CeH,/ Xq + H^G. 

\cO' CO 

The resulting series of compounds are the phthaleins, 
which will be further referred to under the eosins. If 
amido derivatives of the phenols are treated in the same 
manner, amido-phthaleins result, which constitute the series 
of colours known as the rhodamines. Of these the body 
known simply as rhodamine is the type. This is prepared 
by the action of phthaUc anhydride on diethyl-amidophenol. 
The resulting compound, which possesses simultaneously 
acid and basic properties, has the constitution 

0=(CeH3N(CA)20H)2 

CeH / ^o 
CO 

Here, as in the case of magenta, water is eliminated in 
salt formation, the commercial product being the hydro- 



OBGANIC PIGMENTS. 247 

chloride, of the formula CggHgoNgOg, HCl. The simplest 
possible rhodamine, of course, would be that obtained by the 
action of amidophenol on phthalic anhydride, but by the 
introduction of alkyl residues into the amidophenol the 
colour of the resulting body is much intensified, so that the 
compound above described is the body usually known under 
the name, which is in reality generic. 

The amidophenol employed in the preparation of the 
rhodamines is the meta variety. 

Commercial rhodamine forms a red powder, readily 
soluble in water, with a fine crimson colour and a character- 
istic yellow fluorescence, which is best observed in dilute 
solutions. By heating the solution to about 90° this dis- 
appears, and returns when the solution has cooled. 

The free base is precipitated by the addition of caustic 
alkalies, in red flakes, soluble in ether. With stannous 
chloride, rhodamine gives a brilliant scarlet precipitate, which 
in a fine state of division shows a remarkable blue colour, 
somewhat resembling a fluorescence phenomenon. In strong 
sulphuric acid rhodamine dissolves with a yellow colour, 
which changes back to red on dilution with water. Ehoda- 
mine colours are very permanent to light. 

In addition to the normal hydrochloride, the basic hydro- 
chloride is well known under the name of rhodamine B. 
Numerous rhodamines are known, being the corresponding 
compounds of other alkyl-meta-amido-phenols. 

Besides the ordinary rhodamine, the chief of those which 
are used for the production of lakes are the following: 
rhodamine B, the basic hydrochloride of diethyl-w-amido- 
phenol-phthalein ; rhodamine S, the succinein (in which 
succinic anhydride replaces phthalic anhydride) of dimethyl- 
amidophenol; rhodamine 6 G, the ethyl ester of diethyl- 
rhodamine ; and rhodamine 12 G, a still further alkylised 
rhodamine. 



248 CHEMISTBY OF PIGMENTS. 

In preparing the lakes of this group of colours, the best 
results are obtained by the use of tannic acid and tartar 
emetic, as the antimony and tannic acid lake is by far the 
least fugitive of the series, and none of them can be regarded 
as in any way permanent. These lakes are used to a certain 
extent for tinting violet lakes. When used for this purpose 
they are usually precipitated by a salt of phosphoric acid. 
The usual diluent of this lake is a fine variety of barium 
sulphate. 

3. The Azines, (a) Safranines. — These compounds have a 
very complex constitution, all agreeing in containing two 
nitrogen atoms united to each other. The lowest member 
of the group is phenosafranine, the chloride of which pro- 
bably has the constitution * 

NH2.CyH3 I .CgHg.NHg 

\n/ 



The bases themselves are very little known, the salts 
of these being the colouring matters. As a rule they dis- 
solve in strong sulphuric acid, with a fine green colour. 
On adding water the colour gradually changes to a bluish 
green, then to a distinct green. On further dilution violet 
and red shades appear. 

By reduction with a reagent such as tin and hydrochloric 
acid, the colour is discharged, but it returns again on exposure 
to the air, thus differing from the rosaniline colours. 

Alcohol dissolves the colour, forming a red solution with 
a yellow fluorescence. Dilute hydrochloric acid is without 
action, whilst concentrated acid changes the colour to a blue- 
violet. Ammonia and alkalies remove the colour, but without 
much alteration. 

Commercial safranine consists of a mixture of several 
compounds, of which the best defined are the homologues, 
C19H17N4CI, C20H19N4CI and CgiHgiN^Cl. It is prepared in 



OBGANIC PIGMENTS. 249 

various ways, and according to shade is known as : safranine, 
safranine T, aniline pink, safranine extra G, safranine S, 
safranine GGS, safranine GOOO, safranine FF, safranine 
AG and AGT extra. 

Dimethyl-phenosafranine is the base of the colour known 
as fuchsia. Magdala red is a colour which is best classed 
with the safranines, if it does not actually belong to that 
class. It is a very useful colour, known also as naphthalene 
red, napthalene rose, naphthalene scarlet, Sudan red and rose 
pink. It has the formula C30H.21N4CI + H2O. It occurs in 
commerce as a hydrochloride. It is very slightly soluble in 
water, and is characterised by its cherry-red colour in alcohol, 
with a cinnabar-coloured fluorescence. The solution loses its 
fluorescence by the addition of ammonia. It is distinguished 
from eosin by not being dissolved from its compounds by 
alcohol, and by not being easily decomposed by strong alkalies 
or dilute acids. 

Reducing agents decolourise the solutions, the colour 
returning on exposure to the air. 

The only satisfactory lakes of the safranine group are 
those prepared with tartar emetic and tannic acid. They 
are much brighter than the corresponding magenta lakes, 
and are also much faster. 

(b) The Eurhodines. — This group of colours might almost 
be classed with the safranines, as they differ from them only 
in that they are azines in which one atom of hydrogen has 
been replaced by an amido group, whereas in the safranines 
two atoms have been so replaced. The separation of the euro- 
dines into a separate class is due to Otto Witt, whose classifi- 
cation we follow in this respect. The chief colour in this group, 
which is used for the production of lakes, is that known as 
toluylene red, or neutral red. This compound is the hydro- 
•chloride of the base dimethyl-diamidotoluphenazine, of the 
formula Ci5HigN4'HCl, and occurs as a greenish-black powder. 



250 CHEMISTRY OF PIGMENTS. 

easily soluble in water, which turns bluer and finally loses its 
colour on heating with reducing agents. The colour, however,, 
returns on exposure to the air. It gives a fine red solution 
in alcohol, with a brownish fluorescence. With hydrochloric 
acid its solution becomes blue. It forms a^ good lake with 
tannic acid and tartar emetic, which has a blue-red tone. 
The closely allied neutral violet, of the formula Cj^Hj^N^HCl,. 
is a homologue of the above colour, being the hydrochloride 
of dimethyl-diamidophenazine. It is a violet colour, but the 
tannic acid and tartar emetic lake is of a fine red-violet tint. 

4. The SuLphonated Azo-compounds. — The sulpho acids of the 
azo colours are amongst the most important of all the coal- 
tar colours, not only for lake production, but also for all 
purposes for which the colours are used. They are so 
numerous, their number having increased to such an extent 
of recent years, that it is impossible to do more than give 
short details of the principal of those which are used for the 
production of the more important of the red lakes. 

It is necessary, in order to get a clear idea of the sub- 
stances with which we now have to deal, to understand the 
principles involved in the preparation of the several groups 
comprising the azo colours. The fact that they may now be 
regarded as the most important series 9f the coal-tar colouring 
matters, and have in themselves givcQ a fresh impetus to an 
already important industry, justifies a somewhat fuller treat- 
ment than might at first appear necessary in a technical 
work of the character of the present volume. 

(4) Azo Compounds. — The azo dyes form a well-defined and 
well-understood group of compounds. They are prepared by 
the action of diazo compounds on phenols or amines of the 
aromatic series. The diazo compounds themselves result when 
salts of primary amines of the aromatic series are treated with 
nitrous acid. The typical reaction illustrating this important 
change is that of nitrous acid on aniline, as follows : — 



OBGANIC PIGMENTS. 251 

CeHg. NH2. HCl + HNO2 = CgHg.N : N.Cl + 2H2O 

Aniline hydrochloride Nitrous acid Diazobenzene chloride Water 

If aniline in alcoholic solution be treated with nitrous 
acid, the resulting product is diazoamidobenzene. This 
body may be regarded as due to the previous formation of 
free diazobenzene, which then reacts with another molecule 
of aniline, thus : — 

CgHgNiN.OH + CgHjNa, = CfiHgN : N-NH-CgHj + ttjO. 

Diazoamidobenzene 

The diazo compounds are thus characterised by con- 
taining the group N : N, which is combined with one carbon 
atom and with one atom other than carbon. 

The azo compounds, on the other hand, contain this same 
important group, N : N, but it is combined with two carbon 
atoms, this constituting the difference between the two series 
of bodies. The simplest type of the azo compounds is ordin- 
ary azobenzene CgHgNrNCgH^. 

Azobenzene and its homologues can be obtained by the 
reduction of the nitro derivatives of the corresponding hydro- 
carbons. The most suitable reducing agents are sodium 
amalgam, or zinc and alcoholic potash. The typical reaction 
takes place as follows : — 

2O6H5NO2 + 4H2 = CeHjNiNCgHg + 4H2O. 

The simple azo compounds are usually highly coloured 
bodies, but they are not colouring matters, as they possess 
no power of combining with either acids or bases. The real 
colour bodies employed are amido or hydroxy derivatives of 
the azo compounds. The types of these two series are : — 

CgHgNiNCgH^.NHa Amidoazobenzene 
CgHgNiNCgHj.OH Hydroxyazobenzene 

The amidoazo compounds can be employed as such when 
they possess basic properties, combining with acids, and they 
can also be used in the form of their sulpho acids, when they 



252 CHEMISTRY OF PIGMENTS. 

are of an acid character. The preparation of benzene azo ^ 
naphthylamine will serve as an example of the usual method 
of preparing amidoazo compounds. One molecule of ^ 
naphthylamine is dissolved in dilute hydrochloric acid by the 
aid of heat, filtered from any impurity insoluble in acid, 
very considerably diluted and cooled. One molecule of 
aniline hydrochloride is dissolved in water, and a considerable 
excess of hydrochloric acid added to prevent formation of 
diazoamidobenzene on diazotisation, and one molecule of 
sodium nitrite added slowly to the cooled liquid. This 
solution of diazobenzene hydrochloride is filtered into the 
)8 naphthylamine solution with constant stirring, and the 
mixture allowed to stand for several hours to allow com- 
bination to take place, when a red precipitate of benzene azo 
)8 naphthylamine separates in accordance with the following 
scheme : — 

CeHgN^Cl + C10H7NH2 = CeHgN^OioHeNH^ + HCl. 

Substituting other amines or their sulpho acids for the 
aniline and other amines, or phenols ot their sulpho acids for 
the naphthylamine, we may prepare other azo compounds. 
The hydroxyazo compounds are almost invariably used as 
sulpho acids, and this series of colours is perhaps the chief of all 
those used in the manufacture of coal-tar lakes. Amongst 
the amidoazo colours themselves only one is used to any 
extent for assisting in the production of red lakes. This is 
the well-known dye chrysoidine, a more or less orange 
colour, but which is used to give certain shades to other 
well-defined red lakes. Chrysoidine is the hydrochloride 
of diamidoazobenzene, CcHqN : NC6H3(NH2)2HC1. Being a 
strongly basic colour it can be used to advantage with 
magenta, and in this combination it is known under the 
name of cardinal, a name applied, however, to several other 
colours^ A scarlet is also sold which is a mixture of 



ORGANIC PIGMENTS. 253 

safranine and chrysoidine. The lakes of these colours are 
usually prepared as described under magenta and safranine. 

The oxyazo colours may be said to be now the most 
important of all the coal-tar colours, and owe their existence 
to the researches of the late Peter Greiss, who published 
his investigations on these colours in 1878. Since that time 
the chemistry of this group has advanced to an enormous 
extent, and new colours are constantly being discovered. As 
a general rule these colours are superior to the other earlier 
known compounds, both in brilliancy and in permanence. 

In the following short description of the more important 
of the sulphonated azo colours, it must be remembered that 
in actual practice the colours are not usually the pure com- 
pounds here mentioned, but are composed of a mixture of 
closely similar compounds. The usual initials used to desig- 
nate the intensity of the shade (depending on the exact 

> 

degree of alkylisation, etc., of the parent compound) are added 
where necessary ; these are R ( = roth, red) and G ( = gelb, 
yellow). 

The following are the constitutions and technical names 
of the principal colours : — 

Crocein. — The enormous number of varieties of this 
splendid colour, all of which may be employed according 
to the shade desired, are all closely related compounds. 
Typical amongst them is that known as Crocein 3BX. This 
is the diazo combination of naphthionic acid combined with 
one of the many /3 naphthol-sulphonic acids. Chemically, 
its name is sodium naphthalene-sulphonate-azo /8 naphthol 
a sulphonate of sodium. In addition to this compound the 
following croceins are well defined, all being similar com- 
pounds in which the benzene, toluene and naphthalene groups 
replace one another in various ways. Crocein scarlet 3E 
( = scarlet 4EB), crocein scarlet 7B ( = scarlet 6RB) and 
brilliant crocein, are all diazo compounds of closely related 



^54 CHEMISTEY OF PIGMENTS. 

bodies in combination with one of the naphthol-sulphonic 
acids. 

Biebrich scarlet is one of the most useful compounds. It 
is a combination of the diazo compound of amidoazoben- 
jzene-disulphonic acid and /3-naphthol. Xylidene red is also 
much employed. This is the compound of the diazo deriva- 
tive of xylidene and one of the naphthol-disulphonic acids. 

The xyhdene scarlets are such brilliant and permanent 
colours that they are, to a considerable extent, displacing 
the natural cochineal carmine. 

In preparing the lakes of these hydroxy-sulphonic-azo 
compounds, the best base for general use is alumina. The 
shades produced by the use of this base are more brilliant 
and clear than those made in any other manner. Most of 
the metallic salts yield precipitates with these colours, but 
they are, as a rule, soluble to a certain extent in large excess 
of water ; therefore in their preparation a loss of colour is 
often experienced. As a rule, the colour is largely diluted 
with an inert material, such as sulphate of barium ; in the 
preparation of the diluted colour, it is best to precipitate 
the lake and the barium sulphate from a solution of alum 
and barium chloride simultaneously, as the colour is then 
intimately incorporated with the diluent. As a rule, the lakes 
from this group of colours, as is the case with many others, 
have a somewhat bluish shade when prepared from a single 
compound. It is therefore usual to use a mixture of colours in 
which there is sufficient orange to entirely overcome the blue 
shade. 

Although, as a class, these colours are fairly fast to light, 
it has been observed that their permanence usually increases 
with increase in molecular weight. 

5. The Eosins. — As has been mentioned earlier, phthalic 
anhydride and the phenols possess the power of combina- 
tion, with the formation of a group of bodies known as the 



OBGANIC PIGMENTS. 255 

phthaleins. If, instead of using the monatomic phenols, one 
employs the dihydroxy phenol, resorcinol (meta-dihydroxy- 
benzene), a phthalein of great interest is obtained. The 
reaction taking place is as follows : — 

/ c^ \o 

.00. / iXoagh/ 

\co/ \ I 

\ = 

+ 2H2O 

The resulting compound is fluorescein, a yellowish-red 
powder, which even in the most dilute solution shows an 
intense greenish fluorescence. So intense is its colouring 
power, that whole rivers may be coloured for miles by a 
single pound or so of it. It has indeed been used to trace 
the course of underground streams, and the existence of an 
underground connection between the Danube and the Ach, 
a small river running into the Lake of Constance, has been 
proved by its use. 

The eosins are derivatives of fluorescein, in which a certain 
number of the hydrogen atoms are replaced by halogen 
atoms, that is by chlorine, bromine or iodine, the last-named 
being very expensive ; the usual commercial eosins are 
bromine compounds. The iodine compounds are generally 
termed Erythrosins. The most important of these bodies 
are the following: — 

Eosin (Eosin yellowish, Soluble Eosin, Eosin A, etc.) is 
tetrabrom-fluorescein C2oH8Br405. It comes into commerce 
as its potassium salt, C^^H^rfi^^ -h GHgO. It is then 
marked (in German commerce) Eosin J. It is a reddish 
powder with a yellowish-green reflex. Its solutions are 
intensely rose-coloured, with a very fine green fluorescence. 
Its acid properties are very marked, its salts not being 
decomposed by acetic acid. It combines with metallic 



256 CHEMISTRY OF PIGMENTS. 

oxides, forming very insoluble lakes. Silver -and lead salts; 
give red, aluminium and tin give red-yellow lakes. 

Eosin orange, or Eosin 5 G, is a mixture of the tetrabromo 
with the dibromo compound. 

Erythrosin (Eosin blue shade, Pyrosin E, Dianthin B, 
etc.) is tetraiodo-fluorescein. It closely resembles ordinary 
eosin, but its solutions are not fluorescent. 

Aureosin is a mixture of chlorinated fluoresceins. 

Various bromnitro-fluoresceins are known in commerce ;. 
they are called safrosin or Eosin BN. A mixture of bromnitro- 
and of nitro-fluoresceins is also known as Lutecienne. A 
nitrochlor-fluorescein is sold as Eubeosin. 

Various methyl and ethyl derivatives of the eosins are alsa 
occasionally met with. They are called spirit-soluble eosins,. 
and are sold under such names as Eosin BB, spirit primrose,. 
Eose JB (soluble in spirit). 

Eose Bengale, a favourite colour, is the sodium salt of 
tetraiodo-dichlor-fluorescein. 

Phloxin (Phloxin TA) is the potassium salt of tetrabrom- 
tetrachlor-fluorescein. 

Cyanosin is the potassium salt of the methyl ether of 
tetrabrom-dichlor-fluorescein. 

These colours readily yield lakes with salts of lead^ 
aluminium, zinc, tin, etc., of great colouring and covering 
power, but they are very fugitive. 

Lead salts give the bluest shades, whilst tin and aluminium, 
lakes are of a much more yellow tint. The usual inert matter 
used as a diluent is barium sulphate, but sometimes eosia 
lakes are met with containing nothing but lead salts, both as- 
the precipitant for the lake and as the inert base. 

The now very common '' vermilionettes " are eosine lakes 
with a lead base, mixed either with lead sulphate or with 
barium sulphate. We have frequently met with vermilion,, 
sold as pure, containing up to 50 per cent, of sulphate of lead 



ORGANIC PIGMENTS. 257 

with a small quantity of a lead-eosin lake. The fugitive 
nature of this colour renders such an adulteration very 
pernicious. 

Alizarin Compounds. 

All that is necessary in connection with the alizarin lakes 
for the present purpose has been said under madder lakes, to 
which section the reader is referred. The close relationship of 
the colouring matters of madder to the artificial colours ren- 
ders it more convenient to deal with the two sets of colours 
together. 

Orange and Yellow Lakes. 

The lakes of these colours need only be referred to shortly, 
as the main principles of the chemistry of the groups of colours 
to which they belong have been dealt with at sufficiently full 
length in describing the red lakes. Nearly all the orange 
colours employed for the preparation of lakes are sulphonic 
acids of the azo colours, closely related to the azo reds. Types 
of these are the following : — 

Mandarin (Orange II, Tropoeolin 000 No. 2) is benzene- 
sulphonate of sodium-azo-yS-naphthpl. 

Mandarin GE (Orange T, Orange E) is different from this 
only in the fact that the benzene is replaced by orthotoluene. 

In all respects the principles governing the formation of 
red lakes of this class apply to the orange lakes. An imita- 
tion red lead is often met with, consisting of a lead lake of a 
cheap orange, precipitated together with a large amount of 
barium sulphate. The orange lakes are not very permanent. 
Yellow lakes are not of very frequent occurrence, as the use 
of chrome yellows is very satisfactory, and their production 
is much cheaper than that of the yellow lakes. They are, 
however, used to a certain extent to modify the shades of 

green lakes. The principal colours used are the following :• — 

17 



258 CHEMISTRY OF PIGMENTS. 

The basic colour auramine (imido-tetramethyl-diparadi- 
amidodiphenylmethane). It gives an excellent lake with 
tannic acid and tartar emetic. 

Thioflavine (dehydro - thiotoluidine trimethyl - chloride). 
This also gives good results with tannic acid. 

Amongst the acid yellows used for lakes are the follow- 
ing : Tartrazine : this is the trisodium salt of tartrazinic 
acid. Naphthol yellow. Quinoline yellow and metanil 
yellow. These are often used as simple barium lakes, with 
barium sulphate as a diluent. The colours are, how- 
ever, very fugitive, and better results are obtained when 
metanil yellow, which possesses acid and to a certain 
extent basic properties, is used in the form of a tannic 
acid and barium lake. 

Green and Blue Lakes. 

The majority of the green lakes usually met with are 
made from basic colours of the triphenylmethane group (see 
rosaniline), or from sulpho- acids of basic colours, in which 
both the acid and the amido groups have been neutralised in 
the formation of the lake. A certain number are also made 
from purely acid greens, such as certain sulpho-acids of azine 
or azo-greens, and some alizarin derivatives. 

Methyl green is the most important of the basic greens 
from many points of view. It is the zinc chloride compound 
of the hydrochloride of chlor-methyl-hexamethyl-pararosani- 
line, of the formula Ci9Hi2(CH3)6N3. CI. CH3CI 4- ZnClg + HgO- 
It is readily soluble in water and alcohol, and also in amyl 
alcohol. This last character distinguishes it from benzalde- 
hyde green and its allies. By heat it splits up into methyl 
chloride and methyl violet. Hence, by moistening a filter 
paper with a solution of this colour and strongly drying it, 
the colour turns to a fine violet. Strong hydrochloric acid 



ORGANIC PIGMENTS. 259 

turns the colour yellow, and alkalies and reducing agents 
decolourise the pigment. 

Iodine green closely resembles the last described com- 
pound. It was in former times manufactured by using 
methyl iodide instead of methyl chloride, but the iodine 
compound is seldom met with now, and much of the so- 
called iodine green contains no iodine at all. 

Malachite green (Victoria green, Benzaldehyde green) is 
usually met with as the oxalate or the zinc chloride double 
salt. The free base is tetramethyldiamidotriphenylcarbinol, 
of the formula C(OH) (CeHg) (CeH.N. (CH3)2)2. As is 
usual with this group of colours, water is lost in the process 
of salt formation, and the oxalate has the composition 

Ethyl green is the corresponding ethyl compound. 

Acid green, SOF, is the sodium salt of diethyldibenzyl- 
diamidotriphenylcarbinol trisulphonic acid. This body is 
also known as diamond green and dragon green. 

When the purely basic greens are used the acid used for 
precipitation is arsenious acid, which gives by far the most 
brilliant shade possible. The tannic acid and tartar emetic 
lakes are dull, but at the same time useful for certain pur- 
poses. 

When such colours as diamond green are used, barium 
chloride is a favourite precipitant, but the amido groups in 
the colour should first be saturated with tannic acid or some 
other acid. Sometimes an acid yellow is employed with 
the acid greens to tint the resulting lake, and if picric acid 
be used it also serves the purpose of saturating the amido 
groups present. 

Coerulein is a green colour made by heating gallein (the 
phthalic anhydride compound of pyrogallol) with sulphuric 
acid. Its constitution is not certain, but it is probably an 
anthracene derivative of the formula — 



260. CHEMISTBT OP PIGMENTS. 

/C(C,H,)\ 

It gives very fast, but somewhat dull shades with most 
metallic salts. With chromium salts it gives a splendid dull 
olive green which is as fast to light as any of the alizarin 
greens. 

There are several varieties of alizarin green, of very 
complicated constitution. The principal of these is alizarin 
green G, the parent substance of which has the constitution 

yCOv ,CH = CH 

\go/ \ n = ch 

The actual dye is a mixture of sulpho-acids of this body and 
of tri- and ^en^a-oxyanthraquinone quinoline. Various shades 
are produced according to the degree to which the sulphona- 
tion has gone, and also according to the number of OH 
groups introduced. The others are closely related to this 
body, and their lakes are formed in the same manner as the 
aUzarin reds, which have been described under the madder 
lakes 

There are not a great many blue lakes manufactured, as 
they are, in general, rather fugitive, and the ultramarine and 
Prussian blue colours are so permanent and cheap that they 
are usually preferred to the coal-tar colour lakes. 

The colours, however, from which blue lakes are made 
(and also violet lakes, which are generally very closely related 
to the blue colours) belong to the following series ; (1) The 
triphenyl-methane compounds ; (2) the sulpho acids of those 
compounds ; (3) the azines ; (4) the indulines. A few other 
compounds are occasionally employed. 

If the hydrogen atoms of the amido groups of rosaniline 
or pararosanihne be replaced by organic radicles the colour 
becomes violet or blue. The shade is bluer according as 
there are more hydrogen atoms so replaced. The ethyl de- 



OBGANIC PIGMENTS. 261 

rivatives are of a redder shade, the methyl and benzyl deriva- 
tives less red, and the phenyl derivatives of the finest pure 
blue colour. Of the purely basic blues and violets, the substi- 
tuted magentas are perhaps amongst the best known. 

Aniline blue (spirit soluble blue, gentian blue, opal blue) 
is triphenyl-rosaniline, of the formula C2oHig(C6H5)gN3. The 
commercial blue is a mixture of compounds of various degrees 
of alkylisation, the more highly alkylised being of the bluest 
shades ; it is sold in the form of its hydrochloride. 

Spirit soluble diphenylamine blue, Ci9Hi4(CgH5)3N, is 
identical with the last described compound in chemical com- 
position, except that it is triphenylated j?ara-rosaniline. It 
is not practicable to introduce more than three phenyl 
groups into this series of compounds, but more ethyl and 
methyl groups may be added, the resulting blues being very 
intense. Both series of compounds may be sulphonated, 
and the resulting so-called '' soluble " blues are the most 
generally useful for lake production. In addition to the 
bodies included in the above series, the azine group is 
represented by Nile blue, naphthylene blue and methylene 
blue ; and the indulines by *' neutral blue '*. These will be 
found referred to in the table at the end of the chapter. 

Tartrate of antimony and tannic acid are generally used 
as the precipitants of these blue colours. If hydroxy groups 
are present in the colour base, they should be neutralised by 
the addition of barium hydroxide. Sometimes zinc and 
aluminum salts are used to a small extent. 

Violet lakes in general are treated in the same manner 
as blue lakes, buJb it is to be noted that the most brilliant 
lakes are yielded by the basic violet colours precipitated by 
means of phosphoric acid. 

Gallein, the phthalein of pyrogallic acid, of the formula 
CaoHi^jOy, is largely employed for the manufacture of violet 
lakes, with potassium bichromate and tartar emetic. It 



262 CHEMISTRY OF PIGMENTS. 

yields lakes with a fine " bloom ". With lead acetate it 
gives a fine grey-violet lake. The black lakes, which are 
in reality an intensely blue black, are prepared from certain 
acid azo colours. They are, however, usually mixed with 
certain blacks to modify the shade, and are seldom employed 
by themselves. 

INDIGO. 

The importance of this colour as a dyeing material can- 
not be overestimated, but as a pigment, although it finds a 
certain employment, it is equalled in permanence, without 
losing at all in richness of colour, by some of the cheaper 
blue pigments. Hence, and on account of its high price, it 
is only employed to a limited extent for certain fine work. 
Indigo was until quite recently the product only of certain 
plants ; the artificial preparation of the colour, however, was 
achieved some time ago, Prof. Baeyer, of Munich, taking 
out a patent in 1880 for ** the preparation of derivatives and 
homologues of ortho-nitro-cinnamic acid, and their conversion 
into indigo blue and allied dye stuffs ". This triumph in 
chemical science was met with little more than amusement 
by the indigo planters and traders, but within the last few 
years synthetic indigo — rather dearer, but purer than the 
natural colour — has become a commercial article, and it is 
certain that before very long its price will be reduced as 
easier processes are discovered, as they are sure to be. In 
spite of this the indigo planters go on in the same way that 
they have always done, without, except in rare cases, any 
attempt at improvement in their methods. This has called 
forth a very emphatic warning from Prof. Armstrong, and 
there is little doubt that, unless every help that science 
can afford is rapidly brought to bear on the natural pro- 
duction of indigo, the experience of the madder industry will 
be repeated, in which the production of synthetic alizarin in 



OBGANIC PIGMENTS. 263 

time killed the natural madder production, and threw open 
large tracts of cultivated land for the cultivation of other 
crops. 

The principal members of the leguminous genus, Indigo- 
fera, producing indigo, are I. tinctoria (the most important), 
and I, disperma, anil and argentea. Indigo does not exist 
as such in the plants, but is produced by the action of a 
ferment on a glucoside contained in them, called indican, 
which may be extracted from them by means of cold alcohol 

Indigotin, or indigo blue, as it is often termed, was 
formerly described as of the formula CgHgNO, but is now 
well established as of the formula CigHioNgOg and the con- 
stitution 

/ C Os, .0 O. 



O8H4V yG = C\ yOeH4. 

Pure indigotin may be obtained from commercial indigo, 
which contains from 20 to 90 per cent, of it, by mixing it 
with plaster of Paris and water, spreading the mass on 
an iron plate, and heating it cautiously to sublime the 
indigotin, which may be removed from the surface by a fine 
spatula. It is prepared by the oxidation of indigo-white 
(see below), in a state of fair purity, but to obtain the finest 
specimens of the colour the aid of synthetic methods must be 
invoked. 

Pure indigotin forms fine deep blue crystals with a 
coppery sheen, subliming at about 290° C. It is insoluble in 
water, cold alcohol, ether, and in essential oils, but soluble in 
acetic acid, aniline, and nitrobenzene. It may be purified by 
boiUng it with aniline to saturation, filtering and allowing 
the crystals to be deposited, and then washing them with 
alcohol. It is a neutral body, and is not affected by dilute 
acids or alkalies. As a dye it is largely employed for cloth, 
but in the form of a pigment it has but a limited use, either 



264 CHEMISTET OF PIGMENTS. 

as an intense deep blue, or as a mixed colour with yellows, or 
as a light blue diluted with a white. 

Indigo-white is hydindigotin, or reduced indigo, of the 
formula CigHigNgOg. It is obtained by reducing indigotin 
with any of the usual reducing agents. It is of interest only 
to the dyeing industry, on account of the fact that it dissolves 
easily in alkalies, and the weak compound thus formed, when 
absorbed by the fibre, is decomposed by the latter, and the 
indigo-white is fixed by some unknown constituent. On ex- 
posure to weak oxidising agents (such as the atmosphere), 
the indigo-white is re-oxidised to indigotin, and the fibres 
assume the well-known blue colour. 

Commercial indigo, made from the plants, consists chiefly 
of the body indigotin (see below). To obtain the indigo, the 
plants are chopped — or rather those parts in which the 
colour compounds are found, viz,, the leaves and twigs — and 
immersed in water. After a certain time fermentation has 
gone on to the proper degree, and the water is run off into 
shallow vats, and is well agitated in order to expose it as 
much as possible to the action of the air. The yellow liquid 
assumes a greenish colour, and the indigo separates in a 
pulpy state. The blue pulp is boiled with water in order 
to prevent secondary fermentation setting in, which would 
result in the formation of brown products. After a certain 
time the liquid is filtered and the precipitate pressed, and 
slowly dried in sheds from which the light is excluded as far 
as possible. 

The indigo thus obtained varies very greatly in quality, 
both as far as its content in true indigotin and in the amount 
of mineral impurity it contains. Apart from the plants of 
the IndigofercR, several other species yield the colour, among 
which the best known is the woad plant, Isatis tinctoria, and 
several kinds of orchids also contain it in small quantities. 
The chemistry of the group of compounds belonging to the 



ORGANIC PIGMENTS. 265 

indigotin series is too extensive a subject to be adequately 
dealt with in a work of this kind, and the reader is therefore 
referred to text-books on organic chemistry for fuller details 
than the short account which follows contains. 

Indican, CsgHggNgOg^, is the glucoside from which the 
indigotin is derived. It forms a brown syrup, from which 
the last traces of water cannot be separated without great 
trouble, if indeed it is possible at all to remove them. The 
reaction by which the indigotin and glucose are formed is as 
follows : — 

On treatment with strong sulphuric acid, indigotin yields 
sulphonic acids. The bodies accompanying indigotin in 
•commercial indigo also yield such acids, and the resulting 
mixture of sulpho acids is known as soluble indigo, or indigo 
•carmine. The exact properties of indigo carmine vary 
according to the nature of the initial indigo and to the 
details of manufacture ; with a moderate proportion of 
acid, the principal body formed is a mono-sulphonic acid, 
•CigHgNgOgiSOgH, which, as its sodium salt, is known as 
indigo-purple. With e:^cess of acid, a di-sulphonic acid, 
CigH8N202(S03H)2, known as sulphindigotic acid, is formed. 
The indigo carmine of commerce is the sodium salt of the 
«ulphonated indigo. 

A typical sample of commercial indigo analysed by 
Oiradin was found to be composed as follows : — 

Indigotin, C15H10N2O2 61*4 

Indigo red, CieHioNaOi .^ 1'2 

Indigo brown . , 4*6 

Indiglucin, CgHioOg 1*5 

Ash 19-6 

Water 5*7 

The preparation of synthetic indigo may be achieved in 
•several methods. For the historical details of the synthesis 
iiichter's Organic Chemistry, vol. ii., may be consulted. The 



266 CHEMISTRY OF PIGMENTS. 

commercial synthetic indigo now on the market, which is- 
claimed to contain 97 per cent, of pure indigotin, is prepared 
in the following manner : Naphthalene, CjoHg, is oxidised to- 

phthalic acid, CgH^/ , and this is converted inta 

' phthalimide, C6H4<' ^^ y NH. This is then converted into- 

anthranilic acid, C.U,<^Z^^ , and then into phenylglycine- 

* XNHg 

orthocarboxylic acid, CeH, (^g^ CH. COOH' ^"""^ *^'^ '''*'^ 
indoxylcarboxylic acid, C6H4<^^tt\CH. COOH, which is 
finally converted into indigotin, 

^•■"* \NH/ ^ • ^ \NH /^*^*- 

In analysing indigo it is important to determine the 
amount of moisture and ash, and also the percentage of true 
colouring matter. It depends on circumstances whether it 
is necessary to determine the actual amount of indigotin 
separately from the total amount of colouring matter. 

The moisture in good commercial indigo varies from 
about 3 to 9 per cent., and may be driven off in the usual 
manner by drying at 100** C. 

In good samples the ash falls as low as 2 per cent., but in 
fair commercial samples of undoubted purity it may often 
reach from 5 to 8 per cent. Some of the inferior kinds, such 
as that from Madras, may contain as much as 25 per cent. 

It has been proposed to determine the specific gravity of 
the sample, but in the authors' experience this is without, 
any value in judging the quality of indigo. 

Starch is said to be occasionally used as an adulterant of 
indigo, but the authors have never met with it in any sample 
they have examined. If it is thought necessary to look for 



ORGANIC PIGMENTS. 267 

this body, the best plan is to boil the sample with water, and 
after cooling to test the filtered liquid with a solution of 
iodine, when the well-known blue colour will result. 

According to A. H. Allen, a useful proximate analysis of 
indigo may be effected in the following manner. The sample 
is dried at 100° in order to determine the moisture, and the 
dry residue is treated with hot water, and the residue dried 
and weighed. This gives the amount of impurities soluble 
in water. The residue is then treated with hydrochloric acid 
and then with dilute alkali, the residues being weighed after 
each treatment in order to determine the amount dissolved 
by these solvents. It is then treated with alcohol, and the 
amount dissolved determined. This very fairly represents 
the amount of indigo red, which may be of importance to 
determine, as it modifies the blue shade of the indigo. 

The residue, after allowing for the ash it leaves on igni- 
tion, very fairly represents the amount of indigotin. 

C. T. Lee proposes to determine the amount of true 
indigotin by observing the amount which can be obtained 
by sublimation — a method which is easy to carry out, and 
which yields satisfactory results under certain conditions. A 
more accurate method of determining the amount of true 
indigotin is that based on the reduction of this body to indigo 
white and its subsequent reoxidation by exposure to the air. 
The process recommended by C. Eawson is as follows : One 
gramme of the finely powdered sample is treated in a flask 
with 2 grammes of crystallised ferrous sulphate and 5 gr. of 
caustic soda in 1000 c.c. of water. The flask is closed by 
a cork, which has three perforations, through one of which 
passes a syphon, whilst the other two are used respectively 
for the entrance and exit of a current of coal gas. The con- 
tents of the flask are maintained for about two hours at a 
temperature just below 100° C, and after removing the source 
of heat the insoluble matter is allowed to subside ; 500 c.c- 



268 CHEMISTRY OF PIGMENTS. 

(representing 0*5 gr. of the sample) of the liquid, which is 
made up to 1000 c.c. exactly, after cooling, with well boiled 
distilled water, unless it is preferred to make an allowance 
for the quantity of water lost during the heating of the liquid, 
is then syphoned off and the reduced indigo is oxidised by 
allowing a current of air to pass through the liquid. To com- 
plete the precipitation, the liquid is acidified and the precipi- 
tate of indigotin, together with the indigo-red and the indigo- 
brown, is allowed to subside. The supernatant liquid is 
passed through a tared filter, and the precipitate washed 
several times with hot water by decantation, and then boiled 
with alcohol to dissolve the red and brown colouring matter. 
The alcoholic liquid is then allowed to cool in order to ensure 
the deposition of any traces of dissolved indigotin, and the 
residue then collected on the filter and dried and weighed 
after washing with absolute alcohol. 

There are many other methods for an accurate assay of 
indigo, but for the purpose of the present work it is unneces- 
sary to deal further with the subject. For fuller details of 
the numerous processes, the reader is referred to. Allen's 
€ommercial Organic Analysis, vol. iii., part i., in which a very 
full account of the subject will be found. 

VARIOUS UNCLASSIFIED PIGMENTS. 

Dragon's Blood. 

The ordinary dragon's blood of commerce, which is im- 
ported in the form of sticks or lumps, is a resinous product 
of the fruit of several different plants, of which the chief 
appears to be DcBmonodrops Draco. This product is known 
as palm dragon's blood, and is imported from Southern 
Asia. A very similar, but less esteemed product, is the 
Socotra dragon's blood obtained from the fruits of DraccBna 
Cinnabari. Other products are also used. 



ORGANIC PIGMENTS. 269 

The crude resinous product is of a deep red colour, vary- 
ing much in quaUty, and when powdered forms an intensely 
red powder, which is not used in medicine, but is largely 
employed for colouring varnishes and polishes. It forms the 
basis of the majority of the so-called mahogany stains. As a 
pigment it finds only a limited employment. 

According to Dieterich, the resinous product consists of 
the following compounds : dracoalban, a white amorphous 
powder, softening at 192°, and probably of the composition 
C20H40O4 ; this body occurs to the extent of about •2*5 per cent. ; 
dracoresene, a bright yellow amorphous resin, melting at 74°^ 
occurring to the extent of about 14 per cent. ; red resin, the 
true colouring matter, about 55 to 60 per cent. This body 
consists mainly of the benzoate and the benzoyl-acetdte of a 
complex alcohol, dracoresinotannol, CgHgO. OH. Of these 
esters the former largely preponderates. 

There are in addition small quantities of other resinous 
bodies, and in most samples certain quantities of woody fibre 
and other vegetable matter, and about 8 per cent, of mineral 
matter. 

The powdered resin is of a somewhat high value, and 
is therefore liable to considerable adulteration. The chief 
substances used for the purpose of sophistication are oxide of 
iron, powdered bole, common colophony, and finely powdered 
red Sanders wood. The grosser adulterations, such as iron 
oxide or powdered bole, etc., will be left as a residue when 
the resin is treated with solvents, such as alcohol and ether. 
The microscope will reveal the presence of any appreciable 
quantity of woody fibres, and the iron oxide will be found in 
the ash and can be estimated in the usual manner. 

According to Hirschsohn, the saponification number 
(number of millegrams required to saponify one gram of the 
resin) is about 150. 



270 



CHEMISTBY OF PIGMENTS. 



Gambog^e (Gamboge), 

This pigment is a gum-resin yielded by several trees 
growing in various parts of the Malay Peninsula, and 
in Ceylon. It comes into commerce, as a rule, in the 
form of cylindrical rolls, which are prepared by run- 
ning the exuded juice into hollow bamboo canes. 
When broken the mass of gamboge exhibits a conchoidal 
or vitreous fracture, and is of a fine yellow red colour. 
When powdered the colour is of a very fine yellow. The 
finest qualities of gamboge are very brittle, and are nearly 
odourless ; it has little taste at first, but after a time it 
causes a sensation of acridity in the throat. By the 
successive action of ether and water it is almost entirely 
dissolved. When in the powdered form it is often adulter- 
ated, either with starch or with mineral matter. The former 
adulterant is best tested for by the usual reaction for 
starch. A decoction of the gamboge when cooled does not 
become green when a little solution of iodine is added to 
it, but merely of a tawny colour. Inferior varieties of the 
naass gum-resin often contain appreciable quantities of woody 
fibre, etc., and on grinding this is naturally found in the 
powder. The ash of pure gamboge is usually about 0*5 per 
cent., or even less, and should certainly not exceed 1 per 
cent. If it does the presence of added mineral matter may 
be inferred, and the ash should be carefully examined. A 
number of samples were examined by Christison many years 
ago (Companion to the Botanical Magazine, ii., 233), and he gives 
the following results : — 





Slam Gamboge. 


Ceylon Gamboge. 


Pipe. 


Lump. 


Coarse. 

35 61-4 

142— 17-2 

7-8 19-0 

7-8 220 

7-2 10-6 


Resin 

Soluble gum 
Woody fibre 
Starchy matter 
Moisture 


71-6 74-2 

21-8 24-0 

Traces 

4-8 


64-3 65-0 

19-7 20-7 

4-4— 6-2 

5-0— - 6-2 
4.0_ 4-2 


68-8 72-9 

18-8 20-7 

4-3— 6-8 

Not determined 



OEGANIC PIGMENTS. 271 

Those samples containing starch are obviously adulterated. 

A solution of gamboge is acid in reaction, owing to the 
presence of a peculiar resin acid called cambogic acid. The 
approximate composition of normal gamboge may be regarded 
as follows : Moisture, from 1 to 4 per cent. ; resins, chiefly of 
an acid nature, 65 to 70 per cent. ; gum, from 15 to 25 per 
cent. ; wax, under 5 per cent. ; mineral matter, under 1 per 
cent. The gum resin contains no essential oil. Although 
starch and mineral matter may be regarded as the most 
usual adulterants, samples have been found mixed with 
common resin and with dextrin. 

The quantitative action of caustic alkalies on gamboge 
is a useful criterion of its purity. Several chemists have 
examined the gum-resin from this point of view. According 
to Williams the acid number (number of millegrams of 
caustic potash, KOH, used to neutralise the free acids) of a 
genuine sample was 80*6 ; the ester number 67*2, and the 
total saponification number 147'8. Kremel gives 100*0 for the 
acid, and 56*7 for the ester numbers. Beckurts and Briiche 
give for four samples the following figures : Acid numbers, 
89, 81, 69 and 71 ; for the ester numbers, 61, 50, 43 and 44. 

Gamboge is partly soluble in alcohol, ether and ammonia. 
The ammoniacal solution gives a red precipitate with barium 
salts, yellow with zinc salts, red-yellow with lead salts, and 
brownish-yellow with silver salts. 

Buchner has examined the resin acids of gamboge, and 
although the chemistry of these bodies is but poorly under- 
stood, there is good evidence that the formula for the chief 
of these acids, which is termed cambogic or gambogic acid, is 

Gamboge is, in painting work, chiefly employed as a 
water colour, as a bright yellow, or in admixture with blues, 
to form dull greens. It is very useful as a glazing colour, 
but is not permanent in sunlight. 



272 CHEMISTRY OF PIGMENTS. 

Sepia. 

This dark brown ink-like pigment is contained in the ink 
bag, 'a defensive weapon, of the ordinary cuttle fish. Sepia 
officinalis f of Sepia loligo, and other cephalopoda, the " shells '* 
of which are often thrown up on our sea-beaches. 

The ink obtained from this source, and which the animal 
has the power of ejecting at will, in order either to effect 
its escape in the clouded water, or for offensive purposes, 
was known to the ancients. Horace in his Fourth Satire 
speaks of nigrcB stoccvs loliginis. Aristotle also mentions the 
sepia, but rather as a table delicacy than as a pigment 
bearer. 

The juice, or ink, should be taken from the animal soon 
after capture, as it is Hable to putrefaction, and when dried 
forms a black mass which, according to Prout, whose analysia 
is the only one we have seen, consists of 

Black pigment (melanin) 78*00 

Calcium carbonate 10*40 

Magnesium carbonate 7*00 

Alkaline sulphates and chlorides .... 2*16 

Mucus 0*84 

98*40 

The black pigment is isolated by boiling the dried mass 
with water, hydrochloric acid and ammonium carbonate suc- 
cessively. These menstrua presumably remove the mineral 
matter and mucus, and leave the colour as an insoluble 
residue. 

Sepia is insoluble in water, alcohol and ether, but remains 
suspended in water for a time, hence its use as an ink. Its- 
deposition is accelerated by acids or ammonium chloride^ 
It forms a dark-brown solution with caustic potash, and is 
separated by hydrochloric or sulphuric acids, but not by nitric 
acid. It dissolves in ammonia, but not in alkaline carbonates. 

Sepia is prepared in commerce by saturating the dried 



OBGANIC PIGMENTS. 273 

cuttlefish ink with caustic alkali solution, adding more alkali, 
boiling for half an hour, filtering and precipitating with an 
acid, washing and drying at a gentle heat. It is a fine dark 
brown, used principally in water, and for monochrome work. 

Wa/rm Sepia is prepared by the addition of a redder brown, 
as one of the ferric oxide colours. 

Boman Sepia is sepia mixed with a yellow-brown. 

Indian Yellow. 

Indian yellow (Purree, Piuri, Pioury) is a peculiar pig- 
ment of animal origin, used by the natives of India, and to 
some extent by artists. It is a fairly bright yellow, but not 
so fine a colour as gamboge, and is found in commerce as 
round balls weighing a few ounces. Externally it is of a 
brown or dirty green colour, but bright yellow inside, and 
with a characteristic urinous smell, which is easily accounted 
for. 

Indian yellow is obtained by collecting the urine of cows 
fed on the leaf of the mango plant {Mangifera indica), and 
inspissating it until the yellow separates, when it is collected, 
partially dried over a charcoal fire, and then in the air. The 
cows are trained only to micturate when the labia majorce 
are stroked, and by this means about 3*6 litres of urine per 
cow are collected daily. This amount yields about 50 grams 
of purree. 

Purree consists principally of the magnesium and calcium 
salts of euxanthic acid, CigHigOH. 

Graebe, who did a good deal of work on this pigment, 
gives the composition of a fine sample examined by him as 

Euxanthic acid 51*0 

Silicic acid and alumina 1*5 

Magnesium 4*2 

Calcium 8*4 

Water and volatile matter 39*0 

99-1 

18 



274 CHEMISTEY OF PIGMENTS. 

The value of this pigment appears to depend on the pro- 
portion of euxanthic acid present. Some samples contain 
a considerable amount of evxanthone, CigHgO^, which is a 
pale yellow substance, whereas the acid and its salts are of 
a bright yellow colour. 

The composition of j&ve samples, apparently from MM. 
Lefranc et Cie, of Paris, is given in Thorpe's Dictionary of 
Applied Chemistry : — 



Euxanthic acid 


72-3 


70-96 


4-35 


9-3 


33-34 


Euxanthone 


00 


1-12 


2-80 


7-4 


34-00 


Mg . 


5-35 


4-88 


4-85 


4-60 


3-70 


Ga . 


1'76 


2-43 


2-61 


8-33 


3-70 



As the quality goes down the proportion of magnesium 
euxanthate steadily decreases, and the euxanthone increases. 

On treating Indian yellow with dilute hydrochloric acid, 
and then removing the bases with ammonium carbonate, a 
solution of ammonium euxanthate is obtained, from which 
hydrochloric acid precipitates crystalline euxanthic acid. 
Melting-point, 156° to 158° (with decomposition). On de- 
composition by boiling with dilute acids, dextro-glxicuvojiic 
acid and euxanthone are formed : — 

Dextro-g\\JiC\jccomG acid is CHO(CHOH)4'C02H, and accord- 
ing to Graebe euxanthone is represented by the formula 



OH' —O— 
-CO— 



OH. 



Euxanthic acid would appear to be a glucoside-like com- 
pound of euxanthone. Against this constitution the fact 
that euxanthic acid forms two series of salts, CigHj^OuM' 
and CiyHjgOiiM'g, would appear to militate. 

The magnesium salt, which is the principal constituent 
of purree, is CjgHigOuMg, 5H2O. 



ORGANIC PIGMENTS. 276 

Indian yellow was formerly believed by some (Stenhouse, 
for example) to be of vegetable origin, but this view is evi- 
dently erroneous, as its place of manufacture, Monghyr, in 
Bengal Province, is known. We believe that the peculiar 
feeding which results in the formation of this colour is not 
for the benefit of the cows used, and that they do not survive 
the treatment for long, unless occasionally put ofif the mango 
feed. 

Indian yellow is only used for water colour. 

Bitumen, Asphaltum, Mummy. 

Asphaltum or bitumen was originally obtained from the 
neighbourhood of the Dead Sea, and is a kind of pitch similar 
to that now obtained in great quantity from the great pitch 
lake, Trinidad. From its nature it can only be used in oil 
painting. It is a blackish-brown which both darkens in colour 
and cracks on the painted surface. It is, therefore, though 
once used to a considerable extent, an unsuitable pigment for 
permanent work. Much of the pitch used for black tar, 
varnishes and japans is now obtained from coal tar, being 
the residue left in the retort after the distillation of this sub- 
stance. According to the extent to which the distillation is 
carried it is known as " hard " or ** soft " pitch, and for pro- 
tective work is usually dissolved in hght oils which soon 
evaporate and leave a black glossy surface. 

Mummy is a bituminous product associated with animal 
remains and derives its rather gruesome name from its source, 
the bituminous matter having been used in the process of em- 
balming, and probably altered somewhat in character through 
lapse of time. It is used in oil by artists and is less liable to 
change than asphaltum. It has probably, in keeping so long, 
reached its limits of change. 



INDEX. 



Abney's, Sir W., experiments, 27, 

31. 
Alizarin, 16, 207, 211, 212. 

— lakes, 211. 
Alkannin, 235. 
Amplitude of waves, 2. 
Anchusic acid, 234. 
Anthrapurpurin, 213. 
Arsenic greens, 157. 

— sulphides, 179. 

— yellows, 179. 
Asphaltum, 275. 
Aureolin, 28, 153. 
Aareosin, 25i3. 
Azines, 248. 

Azo compounds, 250. 
Azorubine, 15. 



B. 



Barium sulphate, 99. 
Barytes, 99. 
Bistre, 176. 
Bitumen, 275. 
Black, ivory, 45, 174. 

— lamp, 175. 
Blanc fixe, 99. 
Blue, alizarin, 216. 

aniline, 261. 

— Antwerp, 32. 

— Celestial, 44, 45, 192. 

— Chinese, 45. 

— copper, 163. 

— diphenylamine, 261. 

— indigo, 262. 

— Prussian, 28, 32, 144, 182. 

— ultramarine, 164. 
Brazilein, 232. 
Brazilin, 232. 
Brown, Cappagh, 140. 

— Prussian, 144. 



Brown, purple, 141. 

— Vandyck, 32, 44, 180. 

0. 

Carbon pigments, 173. 
Cardinal, 252. 
Carmine, 28, 32. 

— lake, 32, 197, 210. 
Chocolate, 141. 
Chromates, 116. 

— analysis of, 123. 
Chrome yellow, 32. 
Chromium oxide, 32, 113. 
Chrysoidine, 252. 
Cobalt, 32. 

— brown, 149. 

— colours, 147. 

— oxide, 148. 

— pink, 149. 

— silicates, 151. 
Coerulein, 259. 
Coeruleum, 149. 
Coloured bodies, 1, 9. 
Colours, oil, 61. 

— primary and complementary, 8. 

— water, 53. 
Copper pigments, 153. 
Crimson lakes, 28, 32, 203. 
Crocein, 253. 

D. 

DiCHROISM, 11. 

Diorcellinic acid, 238. 
Dispersion, irrationality of, 6. 

E. 

Enamels, 68, 71. 
Encaustic painting; 60. 
Eosin, 16, 254. 
Erythrin, 237, 238. 



278 



INDEX. 



Erythrol, 237. 
Erythrosin, 256. 
Eurhodines, 249. 
Euxanthic acid, 274. 
Euxanthone, 274. 

F. 

Factory Act, as applied to white 

lead, 82. 
Flavopurpurin, 214. 
Frauenhofer's lines, 3, 4. 
Fresco painting, 56. 
Fuchsia, 249. 
Fuchsine, 13. 



G. 



Gallein, 261. 

Gamboge, 28, 270. 

Garancin, 206. 

Giallolino, 177. 

Glass, stained and painted, 72. 

Green, acid, 16, 259. 

— q^rsenical, 157. 

— bice, 154. 

— Bremen, 155. 

— Brunswick, 45, 126, 162. 

— copper, 153. 

— emerald, 32, 157. 

— ethyl, 259. 

— Guignet's, 114. 

— iodine, 259. 

— malachite, 259. 

— methyl, 258. 

— Mittler's, 114. 

— mountain, 154. 

— Paris, 157. 

— sap, 231. 

— Scheele's, 157. 

— Schweinfurt, 157. 

— verdigris, 160. 
Grenadin, 245. 

H. 

HiEMATIN, 219. 

Hsematoxylin, 217. 



I. 



Indian red, 28, 32, 44, 133. 
Indican, 265. 



Indigo, 17, 32, 262. 

— purple, 265. 

— white, 264. 
Indigotin, 263. 

Iron oxide pigments, 128. 

— analysis of, 145. 

Isorubin, 244. 



E. 



Keramic art, 66, 



L. 



Laccainic acid, 205. 
Lakes, alizarin, 211, 257. 

— alkanet, 210, 234. 

— archil, 210, 237. 

— artificial, 242. 

— azine, 248. 

— azo, 250. 

— blue, 258. 

— Brazil wood, 209, 232. 

— Campeachy, 210, 217. 

— carmine, 32, 197, 210. 

— coal tar, 239. 

— cochineal, 196. 

— 6rimson, 28, 32, 203. 

— eosin, 254. 

— eurhodine, 249. 

— green, 256. 

— lac dye, 205. 

— logwood, 210, 217. 

— madder, 32, 206. 

— magentaj 245. 

— natural, 194. 

— orange, 257. 

— orchil, 210, 237. 

— quercitron, 221. 

— red, 242. 

— rhamnus, 225. 

— rhodamine, 246. 

— safranine, 248. . 

— scarlet, 32, 206. 

— Venice, -210. 

— violet, 261. 

— yellow, 257. 

Laurie, A. P., on white lead, 78. 

Laws of refraction, 9. 

Lead chromates, 116, 117, 119. 

— orange, 40, 43, 119. 

— red, 40, 43, 100. 

— white, 41, 43, 77. 



INDEX. 



279 



Light, diffused, 10. 

— nature of, 1. 

— synthesis of, 7. 

— white, 2. 
Litharge, 102. 
Lithopone, 41, 43. 
Lokao, 231. 

M. 

Magenta, 243. . 

— new, 244. 
Malachite, 154. 
Mandarin, 157. 
Maroon, 245. 
Mars colours, 143. 
Massicot, 102. 
Mercuric chromate, 123. 

— iodide, 112. 
Methyl green, 258. 
Minium, 100. 
Mosaic, 76. 
Mummy, 275. 

N. 

Naples yellow, 176. 

0. 

Ochres, 128. 

— red, 132. 

— yellow, 32, 129. 
Opaque bodies, 9. 
Orange eosin, 256. 

— lead, 40, 43, 119. 
Orcellinic acid, 238. 
Orcinol, 238. 
Orpiment, 179. 

P. 

Paints, antifouling, 37. 
Pastels, crayon, 49, 50. 
Persian berrieSj 226, 230. 
Phloxin, 256. 
Picroerythrin, 238. 
Pigments, application of, 18, 49. 

— artistic uses of, 18 et seq. 

— decorative uses of, 34 et seq. 

— protective uses of, 36 et seq. 
Powders, coloured, 12. 
Purple, French, 239. 

— indigo, 265. 



Purple, oxide, 141. 
Purpurin, 213. 
Purree, 273. 

Q. 

Quercetin, 223, 226, 227, 228, 229. 
Quercitrin, 222. 

B. 

Eays, chemical, 5. 

— heat, 5. 

— light, 5. 

— transmitted, 11. 
Realgar, 179. 

Red, Indian, 28, 32, 44, 133. 
~ light, 139. 

— Magdala, 249. 

— oxide, 141. 

— scarlet, 40, 43. 

— Venetian, 28, 32, 133. 
Rhaminose, 226. 
Rhamnazin, 227, 229. 
Rhamnegin, 227. 
Rhamnetin, 227, 229. 
Rhamnose, 230. 
Rhodamine, 243, 246. 
Rosaniline, 230. » '*-' 
Russell, Dr. (see Abney). 



S. 



Safranines, 248. 
Santaline, 209. 
Sap green, 231. 
Scarlet, Biebrich, 254. 

— naphthalene, 249. 

— R., 15. 

— royal, 112. 
Sepia, 28, 272. 
Siennas, 134. 

— burnt, 32, 46, 136. 

— raw, 32, 135. 
Silver chromate, 122. 
Smaltine, 151. 

Smith, H., 0x^)6 riments on paints, 

38. 
Spectra absorption, 14. 
Spectral colours, simple nature 

of, 7. 
Spectrum, 2, 6. 

— invisible, 4. 

— normal, 5, 6. 



280 



INDEX. 



T. 



Tartrazine, 16, 258. 
Tempera painting, 55. 
Terra verte, 32, 143. 
Thioflavine, 258. 
Transparent bodies, 9. 
Triphenyl - methane derivatives, 
243. 

U. 

Ultramarine, 32, 46, 164. 
Umbers, 134. 

— burnt, 32, 138. 

— raw, 137. 

— Turkey, 45, 137. 

V. 

Vandyck brown, 32, 180. 
Varnishes, asphaltic, 37. 

— oil, 37. 

Venetian red, 28, 32, 133. 
Verdigris, 160. 



Vermilion, 28, 32, 103. 
Vermilionette, 40, 43, 108, 112. 
Violet, methyl, 17. 
Vividian, 114. 

W. 

Water colours, action of light on, 

27, 31. 
Wave length, 2. 
White, enamel, 99. 
Whitening, 99. 

Z. 

Xanthorhamnin, 228. 

Y. 

Yellow, cadmium, 180. 

— Indian, 273. 

— Naples, 176. 

— ochre, 32, 129. 

— royal, 179. 

— Turner's, 177. 



UB?^ 






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Contents. 

Chapters I., Introductory Remarks on the General Nomenclature of Oils, Tallow and 
Greases suitable for Lubrication.— II., Hyrocarboii Oils.— III., Animal and Pish Oils.— 
IV., Compound Oils.— V., Vegretable Oils.— VI.. Lamp Oils.— VII., Bngrine Tallow, 
Solidified Oils and Petroleum Jelly.— VIII., Machinery Oreases: Loco and Anti- 
friction.— IX., Clarifyinsr and Utilisation of Waste Fats, Oils, Tank Bottoms, 
Drainings of Barrels and Drums, Pickings Up, Dregs, etc.— X., Tlie Fixing and 
Cleaning of Oil Tanks, etc.— Appendix and Oeneral Information. 

Press Opinions. 

" This work is written from the standpoint of the oil trade, but its perusal will be found very 
useful by users of machinery and all who have to do with lubricants in any way ."^-Co/Ziery 
Guardian. 

"The properties of the different grades of mineral oil and of the animal and vegetable non- 
drying oils are carefully described, and the author justly insists that the peculiarities of the 
machinery on which the lubricants are to be employ^ must be considered almost before every- 
thing else. . . . The chapters on grease and solidified oils, etc., are excellent." — The Ironmonger. 

SOAPS. A Practical Manual of the Manufacture of Domestic, 
Toilet and other Soaps. By George H. Hurst, F.C.S. Illustrated 
with Sixty-six Engravings. 390 pp. 1898. Price 12s. 6d. ; India and 
Colonies, 13s. 6d. ; Other Countries, 15s. ; strictly net. 

Contents. 

Chapters I., Introductory.— II., Soap-maker's Alkalies.— III., Soap Fats and Oils.— 
IV., Perfumes.— v.. Water as a Soap Material.— VI., Soap Machinery.— VII., Tech- 
nology of Soap-maldng.— VIII., Glycerine in Soap Lyes.— IX., Laying out a Soap 
Factory.— X., Soap Analjvis.- Appendices. 

Press Opinions. 

" We think it is the most practical book on these subjects that has come to us from England 
so far." — American Soap Journal. 

" Much useful infbrmation is conveyed in a convenient and trustworthy manner which will 
appeal to practical soap-makers." — Chemical Trade Journal. 

" Works that deal with manufacturing processes, and applied chemistry in particular, are 
sdways welcome. Especially is this the case when the material presented is so up-to-date as 
we find it here." — Bradford Observer^ 

" The best and most reliable methods of analysis are fully discussed, and form a valuable 
source of reference to any works' chemist. . . . Our verdict is a capitally produced book, and 
one that is badly needed." — Birmingham Post. 

ANIMAL PATS AND OILS: Their Practical Production, 

Purification and Uses for a great Variety of Purposes. Their Pro- 
~ perties, Falsification and Examination. A Handbook for Manufacturers 
of Oil and Fat Products, Soap and Candle Makers, Agriculturists, 
Tanners, Margarine Manufacturers, etc., etc. By Louis Edgar And^s. 
Sixty-two Illustrations. 240 pp. 1898. Demy 8vo. Price 10s. 6d. ; 
India and Colonies, lis. ; Other Countries, 12s.; strictly net. 

Contents. 

Introduction. Occurrence, Ori^m, Properties and Chemical Constitution of Animsd Pats 
Preparation of Animal Pats and Oils. Machinery. Tallow-melting Plant. Extraction Plant. 
Presses. Piltering Apparatus. Butter: Raw Material and Preparation, Properties, Adul- 
terations, Beef Lard or Remelted Butter, Testing. Candle-fish Oil. Mutton-Tallow. Hare 
Pat. Goose Pat. Neatsfoot Oil. Bone Pat: Bone Boiling, Steaming Bones, Extraction, 
Refining. Bone Oil. Artificial Butter: Oleomargarine, Margarine Manufacture in Pranoe, 
Orasso's Process, " Kaiser's Butter," Jahr & Miinzberg's Method, Pilbert's Process, Winter's 
Method. Human Pat. Horse Pat. Beef Marrow. Turtle Oil. Hog|[8 I^ard : Raw Materia], 
Preparation, Properties, Adulterations, Examination. Lard Oil. Pish Oils. Liver Oils. 
Artificial Train OiL Wool Pat : Properties, Purified Wool Pat. Spermaceti : Examination 
of Pats and Oils in Oeneral. 



Press Opinions. 

"The descriptions of technical processes are clear, and the book is well illustrated and 
should prove useful." — Manchester Guardian. 

" It IS a valuable work, not only for the student, but also for the practical manufocturer of 
oil and fat products."— /owrwa/ of the A merican Chemical Society. 

"The work is very fully illustrated, and the style throughout is in strong contrast to that 
employed in many such treatises, being simple and clear. " — Shoe and Leather Record. 

" An important handbook for the * fat industry,' now a large one. The explanation of the 
most scientific processes of production lose nothing of their clearness in the translation." — 
Newcastle Chronicle. 

" The latest and most improved forms of machinery are in all cases indicated, and the many 
advances which have been made during the past years in the methods of producing the more 
common animal fats — lard, tallow and butter — receive due attention." — Glasgow Herald. 

VEGETABLE PATS AND OILS : Their Practical Prepara- 
tion, Purification and Employment for Various Purposes, their Proper- 
ties, Adulteration and Examination. A Handbook for Oil Manufacturers 
and Refiners, Candle, Soap and Lubricating Oil Makers, and the Oil 
and Fat Industry in General. Translated from the German of Louis 
Edgar And^s. 94 Illustrations. 320 pp. 1897. Demy 8vo. Price 
10s. 6d. ; India and Colonies, lis. ; Other Countries, 12s. ; strictly nct» 

Contents. 

Statistical Data. General Properties of the Vegetable Fats and Oils. Estimation of the 
Amount of Oil in Seeds. Table of Vegetable Fats and Oils, with French and German 
Nomenclature, Source and Origin and Percentage of Fat in the Plants from which they are 
Derived. The Preparation of Vegetable Fats and Oils : Storing Oil Seeds ; Cleaning the Seed. 
Apparatus for Gnnding Oil Seeds and Fruits. Installation of Oil and Fat Works. Ex- 
traction Method of Obtaining Oils and Fats. Oil Extraction Installations. Press Moulds. 
Non-drying Vegetable Oils. Vegetable drying Oils. Solid Vegetable Fats. Fruits Yielding 
Oils and Pats. Wool-softening Oils. Soluble Oils. Treatment of the Oil after Leaving the 
Press Improved Methods of Refining with Sulphuric Acid and Zinc Oxide or Lead O^ide. 
Refining with Caustic Alkalies, Ammonia, Carbonates of the Alkalies, Lime. Bleaching Fat» 
and Oils. Practical Experiments on the Treatment of Oils with regard to Refining and 
Bleaching. Testing Oils and Fats. 

Press Opinions. 

"Concerning that and all else within the wide and comprehensive connection involved^ 
this book must be invaluable to every one directly or indirectly interested in the matters it 
treats of." — Commerce. 

"The proprietors of the Oil and Colourman's Journal have not only placed a valuable and 
highly interesting book of reference in the hands of the fats and oils mdustry in' general, but 
have rendered no slight service to experimental and manufacturing chemists." — Manufacturing- 
Chemist. 

IRON . CORROSION, ANTI - POULINQ AND ANTI- 
CORROSIVE PAINTS. By Louis Edgar And^s. 62 Illus- 
trations. 275 pp. Translated from the German. DemySvo. 1900. Pricei 
10s. 6d. ; India and Colonies, lis. ; Other Countries, 12s. ; strictly net. 

, ' Contents. 

Ironrust and its Formation — Protection from Rusting by Paint — Grounding the Iron with 
Linseed Oil, etc. — Testing Paints — Use of Tar for Paintmg on Iron — ^Anti-corrosive Paints — 
Linseed Varnish— Chinese Wood Oil — Lead Pigments — Iron Pigments— Artificial Iron Oxide» 
— Carbon — Preparation of Anti-corrosive Paints — Results of Examination of Several Antf- 
corrosive Paints — Paints for Ship's Bottoms — Anti-fouling Compositions — Various Anti-cor 
rosive and Ship's Paints — Official Standard Specifications for Ironwork Paints — Index. 

. . . Press Opinions. 

"This is a very valuable book, translated from the German, discussing in detail anti-fouling 
and anti-corrosiv» paints." — British Mercury. 

"Will be of great service to paint manufacturers, engineering contractors, ironfounders^ 
shipbuilders and others." — Engineer and Iron Trades A dvertiser. 

" The book before us deals with the subject in a manner at once practical and scientific, and 
is well worthy of the attention of all builders, architects and engineers." — The Builder. 

"The book is very readable and full of valuable information, and bearing in mind the 
importance of the subject treated, it is one which engineers will be well advised to procure at 
an early date." — Railway Engineer. 

" The author goes fully into his subject, and the translator has been successful in repro- 
ducing in another language what he has to say. There are given in the text numerous 
illustrations of the rustmg of iron, prepared in the course of a series of personal experiments 
on the formation of rust."—Toumal of Gas Lighting. 

^ "This work is a very elaborate and useful recond of the various phenomena in connection 
with the corrosion of iron and its protection against corrosion. . . . The book is an exceed- 
ingly useful record of what has been done in connection with iron preservation, and wilt 
undoubtedly prove to be of much value to railway engineers, shipowners, etc." — Fairplay. 



" Herr Andes' book, written purely from a scientific standpoint, will be particularly useful 
to iron manufacturers, shipbuilders and shipowners. . . . The book is beautifully printed on 
good paper, and its appearance does credit to the publishers ; the work of translation has been 
remarkably well done, the language bearing none of those irritating traces of Teutonism which 
disfigure so many English versions of German technical works." — The Ironmonger. 

** This knowledge is conveyed with characteristic German thoroughness in this useful work 
of Herr And6s, wnich loses nothing of clearness in Mr. Salter's excellent translation. The 
causes of rust formation are examined, the proper methods of cleansing the ironwork detailed, 
and the constitution and application of suitable preventative coverings explained. . . . The 
book is a welcome contribution to technological literature, and will be found worthv of the 
careful study of all who are professionally engaged in the arrangement or superintendfence of 
the class of work dealt with." — Western Daily Mercury. 

"The author explains the nature of rust and its formation, and the text is illustrated from 
about fifty photographs. An immense amount of carefully arranged information follows as to 
the best methods or applying anti-corrosive substances and the various pigments most effi- 
cacious for use under all circumstances. The author has evidently thoroughly investigated and 
mastered the subject of iron corrosion, its cause and its prevention ; and we regard his book as 
of the greatest imjportance to bridge-builders and makers and users of structural iron and 
steel. The book is illustrated throughout and is admirably indexed and arranged." — Iron and 
Steel Trades Journal. 

THE MANUFACTURE OF ALUM AND THE SUL- 
PHATES AND OTHER SALTS OF ALUMINA AND 
IRON. Their Uses and Applications as Mordants in Dyeing 
and Calico Printing, and their other Applications in the Arts, Manufac- 
tures, Sanitary Engineering, Agriculture and Horticulture. Translated 
from the French of Lucien Geschwind. 195 Illustrations. Nearly 
400 pp. Royal 8vo. 1901. Price 12s. 6d. ; India and Colonies, 13s. 6d. ; 
Other Countries, 15s. ; strictly net. 

ContentSi 

Part I., Theoretical Stud^ of Aluminium, iron, and Compounds of these Metals. 

— Chapters I., Aluminium and its Compounds. — II., Iron and Iron Compounds. 

Part II., Manufacture of Aluminium Sulphates and Sulphates of Iron.— Chapters III., 
Manufacture of Aluminium Sulphate and the Alums. — IV., Manufacture of Sulphates of Iron. 

Part III., Uses of the Sulphates of Aluminium and Iron.— Chapters V., Uses of 
Aluminium Sulphate and Alums — Application to Wool and Silk — Preparing and using Aluminium 
Acetates — Employment of Aluminium Sulphate in Carbonising Wool — The Manufacture of 
Lake Pigments — Manufacture of Prussian Blue — Hide and Leather Industry — Paper Making — 
Hardening Plaster — Lime Washes — Preparation of Non-inflammable Wood, etc. — Purifica- 
tion of Waste Waters.— VI., Uses and Applications of Ferrous Sulphate and Ferric 
Sulphates. — Dyeing — ManuiFacture of Pigments — Writing Inks — Purification of Lighting Gas 
— Agriculture — Cotton Dyeing — Disinfectant — Purifying Waste Liquors — Manufacture of 
Nordhausen Sulphuric Acid — Fertilising. 

Part IV., Chemical Characteristics of Iron and Aluminium.— Analysis of Various 
Aluminous or Ferruginous Products.— Chapter VII., Aluminium.— Analvsinflr Aluminium 
Products. — Alunite Alumina — Sodium Aluminate — Aluminium Sulphate. Chapter VIII., Iron. 
— ^Analytical Characteristics of Iron Salts — Analysis of Pyritic Lignite — Ferrous and Ferric 
Sulphates — Rouil Mordant — Index. 

MANUAL OF AGRICULTURAL CHEMISTRY. By 

Herbert Ingle, F.I.C, Lecturer on Agricultural Chemistry, the 
Yorkshire College; Lecturer in the Victoria University. [In the press. 

Contents. 

Chapters I., Introduction. — II., The Atmosphere. — III., The Soil. — IV., The Reactions 
occurring in Soils. — V., The Analysis of Soils. — VI., Manures, Natural. — VII., Manures (con- 
tinued). — ^VIIL, The Analysis of Manures. — IX., The Constituents of Plants. — X., The Plant. — 
XL, Crops.— XII., The Animal. 

LUBRICATING OILS, FATS AND GREASES: Their 

Origin, Preparation, Properties, Uses and Analyses. A Handbook for 
Oil Manufiacturers, Refiners and Merchants, and the Oil and Pat 
Industry in General. By George H. Hurst, F.C.S. Second Edition. 
Sixty-five Illustrations. 313 pp. Demy Svo. 1901. Price 10s. 6d. ; 
India and Colonies, lis. ; Other Countries, 12s. ; strictly net. 

Contents. 

ji Chapters I., Introductory. Oils and Pats, Patty Oils and Pats, Hydrocarbon Oils, Uses 
of Oils. — II., Hydrocarbon Oils. Distillation, Simple Distillation, Destructive Distillation, 
Products of Distillation, Hydrocarbons, Paraffins, Olefins, Napthenes. — III., Scotch Shalo 
Otis. Scotch Shales, Distillation of Scotch Oils, Shale Retorts, Products of Distilling Shales 



Separating Products, Treating Crude Shale Oil, Refining Shale Oil, Shale Oil Stills, Shale 
Naphtha Burning Oils, Lubricating Oils, Wax. — IV., Petroleuill. Occurrence, Geology, Origin, 
Composition, Extraction, Refining, Petroleum Stills, Petroleum Products, Cylinder Oils, 
Russian Petroleum, Deblooming Mineral Oils.— V., Vegetable and Animal Oils. Intro- 
duction, Chemical Composition of Oils and Pats, Patty Acids, Glycerine, Extraction of Animal 
and Vegetable Pats and Oils, Animal Oils, Vegetable Oils, Rendering, Pressing, Refining, 
Bleaching, Tallow, Tallow Oil, Lard Oil, Neatsfoot Oil, Palm Oil, Palm Nut On, Cocoanut 
Oil, Castor Oil, Olive Oil, Rape and Colza Oils, Arachis Oil, Niger Seed Oil, Sperm Oils, 
Whale Oil, Seal Oil, Brown Oils, Lardine, Thickened Rape Oil.— VI., Testing and Adultera- 
tion of Oils. Specific Gravity, Alkali Tests, Sulphuric Acid Tests, Pree Acids in Oils, Vis- 
cosity Tests, Plash and Pire Tests, Evaporation Tests, Iodine and Bromide Tests, Elaidin 
Test, Melting Point of Pat, Testing Machines. — ^VII., Lubricating Greases. Roain Oil, 
Anthracene Oil, Making Greases, Testing and Analysis of Greases. — VIII., Lubrication. 
Priction and Lubrication, Lubricant, Lubrication of Ordinary Machinery, Spontaneous Com- 
bustion of Oils, Stainless Oils, Lubrication of Engine Cylinders, Cylinder Oils. — Appendices. 
A. Table of Baume's Hydrometer — B. Table of Thermometric Degrees — C. Table of Specific 
Gravities of Oils — index. 

Press Opinions. 

" The book is well printed, and is a credit alike to author, printer and puhUsher."— Textile 
Mercury. 

" It will be a valuable addition to the technical library of every steam user's establishment." 
— Machinery Market. 

" Mr. Hurst has in this work supplied a practical treatise which should prove of especial 
value to oil dealers, and also, though in a less degree, to oil users." — Textile Manufacturer. 

" This is a clear and concise treatment of the method of manufacturing and refining lubri- 
cating oils. . . . The book is one which is well worthy the attention of readers who are users 
of oil."— Textile Recorder. 

" We have no hesitation in saying that in our opinion this book ought to be very useful to 
all those who are interested in oils, whether as manufacturers or users of lubricants, or to 
those chemipts or engineers whose duty it may be to report upon the suitability of the same 
for any particular class of work." — Engineer. 

" The author is widely known and highly respected as an authority on the chemistry of oils 
and the technics of lubrication, and it is safe to say that no work of similar interest or equal 
value to the general oil-selling and consuming public has heretofore appeared in the English 
language." — Drugs, Oils and Paints, U.S.A. 

** This valuable and useful work, which is both scientific and practical, has been written 
with a view of supplying those who deal in and use oils, etc., for the purpose of lubrication, 
with some information respecting the special properties of the various products which cause 
these various oils to be of value as lubricants." — Industries and Iron. 

" A mere glance at the table of contents is sufficient to show how various are the conditions 
to which these materials have to be applied, how much knowledge is required for the selection 
of the ri^ht kind for each particular purpose, and how by processes of mixture or manufacture 
the requisite qualities are obtained in each case." — Manchester Guardian. 

AMMONIA AND ITS COMPOUNDS : Their Manufacture 
and Uses. By Camille Vincent, Professor at the Central School of 
Arts and Manufactures, Paris. Translated from the French by M. J. 
Salter. Royal 8vo. 113 pp. 1901. Thirty-two Illustrations. Price 
5s. ; India and Colonies, 5s. 6d. ; Other Countries, 6s. ; strictly net. 

Contents. 

Chapters I., General Considerations : Sections 1. Various Sources of Ammoniacal 
Products; 2. Human Urine as a Source of Ammonia. II., Extraction of Ammoniacal 
Products from Sewas^e : Sections 1. Preliminary Treatment of Excreta in the Settlin&| 
Tanks — The Lencauchez Process, The Bilange Process, The Kuentz Process ; 2. Treatment ot 
the Clarified Liquors for the Manufacture or Ammonium Sulphate — The Piguera Process and 
Apparatus, Apparatus of Margueritte and Sourdeval, The Lair Apparatus, Apparatus of Sintier 
and Muh6, Apparatus of Bilange, The Kuentz Process, Process and Apparatus of Hennebutte 
and De Vaur^al; 3. Treatment of Entire Sewage — Chevalet's Apparatus, Paul Mallet's 
Apparatus, Lencauchez's Apparatus. III., Extraction of Ammonia from Qas Liquor: 
Sections L Clarification of Gas Liquor; 2. Manufacture of Ammonium Sulphate — A. Mallet's 
Apparatus, A. Mallet's Modified Apparatus, Paul Mallet's Apparatus, Chevalet's Apparatus, 
Griineberg's Apparatus ; 3. Concentration of Gas Liquor — Solvay's Apparatus, Kuentz's 
Apparatus, Griineberg's Apparatus. IV., Manufacture of Ammoniacal Compounds from 
Bones, Nitrogenous Waste, Beetroot Wash and Peat : Sections 1. Ammonia from Bones ; 
2. Ammonia from Nitrogenous Waste Materials; 3. Ammonia from Beetroot Wash (Vinasse); 
4. Ammonia from Peat — Treatment of the Ammoniacal Liquors. V., Manufacture of 
Caustic Ammonia, and Ammonium Chloride, Phosphate and Carbonate : Sections 1. 
Manufacture of Caustic Ammonia ; 2. Manufacture of Ammonium Chloride — From Fermented 
Urine, Process of the Lesage Company, Kuentz's Process ; From Gas Liquor, English Process, 
Kuentz's Process; Prom the Dry Distillation of Animal Matter; From Ammonium Sulphate, 
Sublimation ; 3. Ammonium Phosphates ; 4. Carbonates of Ammonium — Sesquicarbonate from 
Animal Matter, English Process, Uses. VI., Recovery of Ammonia from the Ammonia- 
Soda Mother Liquors : Sections 1. General Considerations; 2. Apparatus of Schloesing and 
Holland ; 3. Apparatus of the Soci€t6 Anonyme de I'Est. — Index. 



THE MANUFACTURE OF VARNISHES, OIL RE- 
FINING AND BOILING, AND KINDRED INDUS- 
TRIES. Describing the Manufacture of Spirit Varnishes 
and Oil Varnishes ; Raw Materials : Resins, Solvents and Colouring 
Principles ; Drying Oils : their Properties, Applications and Prepara- 
tion by both Hot and Cold Processes ; Manufocture, Employment and 
Testing of Different Varnishes. Translated from the French of Ach. 
LiVACHE, Ingenieur Civil des Mines. Greatly Extended and Adapted 
to English Practice, with numerous Original Recipes. By John 
Geddes McIntosh, Lecturer on Oils, Colours and Varnishes, Regent 
Street Polytechnic. Twenty-seven Illustrations. 400 pp. Demy 8vo. 
1899. Price 12s. 6d. ; India and Colonies, Ids. 6d. ; Other Countries, 
15s. ; strictly net. 

Contents. 

I. Resins : Gum Resins, Oleo Resins and Balsams, Commercial Varieties, Source, Collec- 
tion, Characteristics, Chemical Properties, Physical Properties, Hardness, Adulterations. 
Appropriate Solvents, Special Treatment, Special Use. — II. Solvents: Natural, Artificial, 
Manunicture, Storage, Special Use. — III. Colouring : Principles, (1) Vegetable, (2) Coal Tar, 
(3) Coloured Resinates, (4) Coloured Oleates and Linoleates. — Gum Running: |Fumacc«, 
Bridges, Flues, Chimney Shafts, Melting Pots, Condensers, Boiline or Mixing Pans, Copper 
V^essels, Iron Vessels (Cast), Iron Vessels (Wrought), Iron Vessels (Silvered), Iron Vessels 
Enamelled), Steam Superheated Plant, Hot-air Plant. — Spirit Varnish Manufacture: Cold 
Solution Plant, Mechanical Agitators, Hot Solution Plant, Jacketted Pans, Mechanical 
\gitators, Clarification and Filtration, Bleaching Plant, Storage Plant. — Manu^cture, Char- 
acteristics and Uses of the Spirit Varnishes yielded by : Amber, Copal, Dammar, Shellac, 
Mastic, Sandarac, Rosin, Asphalt, India Rubber, Gutta Percha, Collodion, Celluloid, Resin- 
ates, Oleates. — Manufacture of Varnish Stains. — Manufacture of Lacquers. — Manufocture of 
Spirit Enamels. — Analysis of Spirit Varnishes. — Physical and Chemical Constants of Resins. 
— Table of Solubility of Resins in different Menstrua. — Systematic qualitative Analysis of 
Resins, Hirschop's tables. — Drying Oils : Oil Crushing Plant, Oil Extraction Plant, Individual 
Oils, Special Treatment of Linseed Oil, Poppyseed Oil, Walnut Oil, Hempseed Oil, Llamantia 
Oil, Japanese Wood Oil, Gurjun Balsam, Climatic Influence on Seed and Oil.— Oil Refining: 
Processes, Thenard's, Liebig's, Filtration, Storage, Old Tanked Oil. — Oil Boiling : Fire Boil- 
ng Plant, Steam Boiling Plant, Hot-Air Plant, Air Pumps, Mechanical Agitators, Vincent's 
Process, Hadfield's Patent, Storer's Patent, Walton's Processes, Continental Processes, Pale 
Boiled Oil, Double Boiled Oil, Hartley and Blenkinsop's Process. — Driers: Manufacture, 
Special Individual Use of (1) Litharge, (2) Sugar of Lead, (3) Red Lead, (4) Lead Borate, 
(S) Lead Linoleate, (6) Lead Resinate, (7) Black Oxide of Manganese, (8) Manganese Acetate, 
(9) Manganese Borate, (10) Manganese Resinate, (11) Manganese Linoleate, Mixed Resinates 
and Linoleates, Manganese and Lead, Zinc Sulphate, Terebine, Liquid Driers. — Solidified 
Boiled Oil. — Manufacture of Linoleum. — Manufacture of India Rubber Substitutes. — Printing 
Ink Manufacture— Lithographic Ink Manufacture. — Manufacture of Oil Varnishes. — Running j 
and Special Treatment of Amber, Copal, Kauri, Manilla. — ^Addition of Oil to Resin. — Addition 
of Resin to Oil. — Mixed Processes. — Solution in Cold of previously Fused Resin. — Dissolving 
Resins in Oil, etc., under pressure. —Filtration. — Clarification. — Storage. — Ageing. — Coach- i 
makers' Varnishes and Japans.— Oak Varnishes. — Japanners' Stoving Varnishes. — Japanners' 
Gold Size. — Brunswick Black. — Various Oil Varnishes. — Oil-Varnish Stains. — Varnishes for 
'* Enamels ".-India Rubber Varnishes. — Varnishes Analysis : Processes, Matching. — ^Faults in 
Varnishes : Cause, Prevention. — Experiments and Exercises. 

Press Opinions. 

" There is no question that this is a useful book." — Chemist and Druggist. 

" The diffierent formulae which are quoted appear to be fa^* more ' practical ' than such as 
are usually to be found in text-books ; and assuming that the original was published two or 
three years a^o, and was only slightly behindhand in its information, the present volume gives 
a fair msight mto the position of the varnish industry." — The Ironmonger. 

m 

Letter from the Teacher of a Technical Class. 

" As a teacher I have often been consulted as to the best work on Varnish Manufacture 
and kindred industries, and have been at a loss in recommending a really practical one. It is 
therefore with pleasure that I can now testify as to the merits of the book on these subjects | 
by A. Livache and J. G. Mcintosh recently published by' Messrs. Scott, Greenwood & Co. In j 
my opinion no varnish maker ought to be without it ; moreover, it is the best text-book that I 
could be put into the hands of trade students or beginners. It has also the merits of being 
thoroughly up-to-date and of possessing a remarkabfy comprehensive index. I can conscien- 
tiously recommend it to my students and trade friends."— -Charles Harrison, Lecturer on 
the Manufacture of Painters* Oils, Colours and Varnishes, Borough Polytechnic, Borough 
Road, S.E. 

"nrdMay, 1899" 



THE MANUFACTURE OF LAKE PIGMENTS FROM 
ARTIFICIAL COLOURS. By Francis H. Jennison, 
F.I.C., F.C.S. Sixteen Coloured Plates, ehowingr Specimens of 
Eifftity-nine Colours, specially prepared from the Recipes griven 

In the Book. 136 pp. Demy 8vo. 1900. Price 7s. 6d. ; India and 
Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 

Contents. 

Chapters I., Introduction. — II., The Groups of the Artificial Colouring Matters. — III., Th«s 
Nature and Manipulation of Artificial Colours. — IV., Lake-formintf Bodies for Acid Colours. — 
v.. Lake-forming Bodies' Basic Colours.— VI., Lake Bases. — VII., The Principles of Lake 
Formation. — VIII., Red Lakes. — IX., Orange, Yellow, Green, Blue, Violet and Black Lakes. — 
X., The Production of Insoluble Azo Colours in the Form of Pigments. — XI., The General 
Properties of Lakes Produced from Artificial Colours. — XII., Washing, Filtering and Fin- 
ishing. — XIII., Matching and Testing Lake Pigments. — Index. 

Press Opinions. 

" It is evidently the result of prolonged research, and cannot but prove a valuable con- 
sulting work to those engaged in the industry." — Derby Mercury. 

" The practical portion of the volume is the one which will especially commend itself, as 
that is the part of the subject which most readers would buy the book for." — Chemist and 
Druggist. 

" This work just issued is a very valuable treatise on the manufacture of lake pigments of 
the coal-tar series principally. The plan adopted by the author in writing up the subject 
enables the manufacture to be very readily understood. . . . The general properties of lakes 
produced from artificial colours, washing, filtering and finishing, and matching and testing 
lake pigments are well and exhaustively described, so that no manufacturer or user of lake 
pigments can well afford to be without this work." — Chemical Trade Journal. 

" This is undoubtedly a book which will occupy a very high place amongst technical works, 
and will prove of exceptional value to all whom it immediately concerns. We have no 
hesitation in recommending it as one of the best works of its class we have ever read. Mr. 
Jennison has set about his task with a lucid style, and with a complete mastery of his subject. 
. . We do not think students of the technical side of the paint and colour industry can 
possibly spend 7s. 6d. in a more profitable way than by buying this publication." — Eastern 
Morning News. 



THE TESTING AND VALUATION OP RAW MATE- 
RIALS USED IN PAINT AND COLOUR MANU- 
FACTURE. By M. W. Jones, F.C.S. A Book lor the 

Laboratories of Colour Works. 88 pp. Crown 8vo. 1900. Price 5s. ; 
India and Colonies, 5s. 6d. ; Other Countries, 6s. ; strictly net. 

Contents. 

Aluminium Compounds. China Clay. Iron Compounds. Potassium Compounds. Sodium 
Compounds. Ammonium Hydrate. Acids. Chromium Compounds. Tin Compounds. Cop- 
per Compounds. Lead Compounds. Zinc Compounds. Manganese Compounds. Arsenic 
Compounds. Antimony Compounds. Calcium Compounds. Barium Compounds. Cadmium 
Compounds. Mercury Compounds. Ultramarine. Cobalt and Carbon Compounds. Oils 
Index. 

Press Opinions. 

" Though this excellent little work can appeal only to a limited class, the chemists in colour 
MTorks, yet it will appeal to them very strongly indeed, for it will put them on the track of 
short, rapid, and yet approximately, accurate methods of testing the comparative value of 
competing samples of raw material used in paint and colour manufacture." — North British 
Daily Mail, 

" This little text-book is intended to supplement the larger and more comprehensive works 
on the subject, and it embodies the result of Mr. Jones' experiments and experiences, extend- 
ng over a long period. It gives, under separate headings, the principal ingredients and im- 
purities found m the raw materials, and is a handy work of reference for ascertaining what is 
valuable or detrimental in the sample under examination." — Blackburn Times. 

"There is no attempt at literary adornment nor straining after literary effect, but the 
lessons are imparted in simple and concise language. This is just what a text-book should 
be. . . . The treatise is certainly most useful, and bears internal evidence of being the results 
of actual work in a busy manufactory and not of ephemeral cramming in a technical school. 
The chapter arrangement is good, the index satisfactory, and the book is altogether one which 
the practical chemist should keep as accessible to his crucibles and filter paper." — Manchester 
Courier. 



8 

THE CHEMISTRY OF ESSENTIAL OILS AND ARTL 
FICIAL PERFUMES. By Ernest J. Parry, B.Sc. 

(Lond.), F.I.C., F.C.S. Illustrated with Twenty Engravings. 400 pp. 
1899. Demy 8vo. Price 128. 6d. ; India and Colonies, 13s. 6d. ; Other 
Countries, 15s. ; strictly net. 

Contents. 

Chapters I., The General Properties of Essential Oils. — II., Compounds occurring 
In Essential Oils.— III., The Preparation of Essential Oils.— IV., The Analysis of 
Essential Oils.— V., Systematic Study of the Essential Oils.— VI., Terpeneless Oils.— 
VII., The Chemistry of Artificial Perfumes.— Appendix : Table of Constants. 

Press Opinions. 

" There can be no doubt that the publication will take a high place in the list of scientific 
text-books." — London Argus 

" We can heartily recommend this volume to all interested in the subject of essential oils 
from the scientific or the commercial standpoint." — British and Colonial Druggist. 

" Mr. Parry has done good service in carefully collecting and marshalling the results of the 
numerous researches published in various parts of the world." — Pharmaceutical Journal. 

" At various times monographs have been pnnted by individual workers, but it may safely 
be said that Mr. Parry is the first in these latter days to deal with the subject in an adequate 
manner. His book is well conceived and well written. . . . He is known to have sound practi* 
cal experience in analytical methods, and he has apparently taken pains to make himself aufait 
with the commercial aspects of the subject." — Chemist and Druggtst. 

" Mr. Parry's reputation as a scientist is fully established, and we can therefore accept any 
work emanating from his pen as being of the greatest practical value. We have perused the 
work before us with much care, and are convinced that the contents will be found most service- 
able and its publication most opportune. . . . He avoids unnecessary details, but includes 
everything that is essential to systematic treatment, while he attempts no more ' than to give 
an outline of the principles involved '. . . . We congratulate Mr. Parry on the scientific value 
of his work, and hope that if the progress of the colonies in the manufacture of essential oils 
and perfumes equals what we are justified in expecting, it will become an Australian hand-book, 
everywhere appreciated." — The Australian Brewers' Journal. 

DRYING OILS, BOILED OIL AND SOLID AND 

LIQUID DRIERS. By L. E. Andes. A Practical Work 
for Manufacturers of Oils, Varnishes, Printing Inks, Oilcloth and Lino- 
leum, Oilcakes, Paints, etc. Expressly Written for this Series of Special 
Technical Books, and the Publishers hold the Copyright for English and 
Foreign Editions. Forty-two Illustrations. 360 pp. 1901. Demy 8vo. 
Price 12s. 6d. ; India and Colonies, 13s. 6d. ; Other Countries, 15s. ; 
strictly net. 

Contents. 

Chapters I., General Chemical and Physical Properties of the Drying Oils ; Cause of the 
Drying Property ; Absorption of Oxygen ; Behaviour towards Metallic Oxides, etc. — II., The 
Properties of and Methods for obtainmg the Drying Oils. — III., Production of the Dtying Oils 
by Expression and Extraction ; Refining and Bleaching ; Oil Cakes and Meal ; The Rcmning 
and Bleaching of the Drying Oils ; The Bleaching of Linseed Oil. — IV., The Manufacture dr 
Boiled Oil ; The Preparation of Drying Oils for Use in the Grinding of Paints and Artists' 
Colours and in the Manufacture of Varnishes by Heating over a Fire or by Steam, by the Cold 
Process, by the Action of Air, and by Means of the Electric Current; The Driers used in 
Boiling Linseed Oil ; The Manufacture of Boiled Oil and the Apparatus therefor ; Livache's 
Process for Preparing a Good Drying Oil and its Practical Application. — ^V., The Preparation 
of Varnishes for Letterpress, Lithographic and Copperplate Printing, for Oilcloth and Water- 
proof Fabrics ; The Manufacture or Thickened Linseed Oil, Burnt Oil, Stand Oil by Fire Heat, 
Superheated Steam, and by a Current of Air. — VI., Behaviour of the Drying Oils and Boiled 
Oils towards Atmospheric Influences, Water, Acids and Alkalies. — VIL, Boiled Oil Substitutes. 
— VIIL, The Manufacture of Solid and Liquid Driers from Linseed Oil and Rosin; Linolic 
Acid Compounds of the Driers. — IX., The Adulteration and Examination of the Drying Oils 
and Boiled Oil. 

REISSUE OF CHEMICAL ESSAYS OP C. W. 
SCHEELE. First Published in English in 1786. Trans- 
lated from the Academy of Sciences at Stockholm, with Additions. 300 
pp. Demy 8vo. 1901. Price 5s.; India and Colonies, 5s. 6d. ; Other 
Countries, 6s. ; strictly net. 

Contents. 

Memoir: C. W. Scheele and his work (written for this edition).— Chapters I., On Fluor 
Mineral and its Acid. — II., On Fluor Mineral. — IIL, Chemical Investigation of Fluor Acid, 
with a View to the Earth which it Yields, by Mr. Wiegler. — IV., Additional Infbrmatioo 
Concerning Fluor Minerals. — V., On Manganese, Magnesium, or Majgnesia Vitrariorum. 
— VI., On Arsenic and its Acid. — VII., Remarks upon Salts of Benzoin. — VIIL, On Silex. 
Clay and Alum. — IX., Analysis of the Calculus Vesical. — X., Method of Preparing Mercurius 



I 



Dulcis Via Humida. — XI., Cheaper and more Convenient Method of Preparing Pulvis 
Aiffurothl. — XII., Experiments upon Molybdaena. — ^XIIl., Experiments on Plumbago. — XIV., 
Method of Preparing a New Green Colour. — XV., Of the DMomposition of Neutral Salts by 
Unslaked Lime and Iron. — XVI., On the Quantity of Pure Air which is Daily Present in our 
Atmosphere. — XVII., On Milk and its Acid. — XVIII., On the Acid of Saccharum Lactis. — 
XIX., On the Constituent Parts of Lapis Ponderosus or Tungsten. — XX., Experiments and 
Observations on Ether. 

GLUE AND GLUE TESTING. By Samuel Rideal, D.Sc. 

Lond., F.I.C. Fourteen Engravings. 144 pp. DemySvo. 1900. Price 
10s. 6d. ; India and Colonies, lis. ; Other Countries, 12s.; strictly net. 

Contents. 

Chapters I., Constitution and Properties : I>efinitions and Sources, Gelatine, Chondrin 
and Allied Bodies, Physical and Chemical Properties, Classification, Grades and Commercial 
Varieties. — II., Raw Materials and Manufacture : Glue Stock, Lining, Extraction, Washing 
and Clarifying, Filter Presses, Water Supply, Use of Alkalies, Action of Bacteria and of 
Antiseptics, Various Processes, Cleansing, Forming, Drying, Crushing, etc., Secondary Pro- 
ducts. — III., Uses of Qiue : Selection and Preparation for Use, Carpentry, Veneering, 
Paper-Making, Bookbinding, Printing Rollers, Hectographs, Match Manufacture, Sandpaper, 
etc.. Substitutes for other Materials, Artificial Leather 2M>d Caoutchouc. — IV., Qelatine: 
General Characters, Liquid Gelatine, Photographic Uses, Size, Tanno-, Chrome and Formo- 
ijelatine. Artificial Silk, Cements, Pneumatic Tyres, Culinary, Meat Extracts, Isinglass, Medi- 
cinal and other Uses, Bacteriology. — ^V., Qiue Testing: Review of Processes, Chemical 
Examination, Adulteration, Physical Tests, Valuation of Raw Materials. — VI., Commercial 



Press Opinions. 

"This work is of the highest technical character, and gives not only a full and practical ac- 
count of the raw materials and manufacture of glues, gelatines and similar substances, but 
gives many hints and information on the use of such substances in veneering, carpentry and 
many other purposes. Many tests are given for glue in different stages of the progress of its 
manufacture, and the commercial value of a commodity so much in general use is exemplified 
by statistics and figures. It is certainly a valuable treatise upon an article for which very 
little literature in any form has previously been obtainable." — Carpenter and Builder. 

** Books on the art of glue making are more than usually scarce, and users of that article, 
as well as those who may be tempted to embark in the mdustry, should therefore welcome 
this book by Dr. Samuel Rideal, a Fellow of the Institute of Chemistry, and a leading authority. 
In this book he has collected the more important facts connected with the manufacture of glue 
snd allied products, and stated the experience he has gained in examining various commercial 
samples during the past ten years. . . . Dr. Rideal's book must be regarded as a valuable con- 
tribution to other technical literature, which manufacturers, merchants and users may study 
with profit." — British Trade Journal. 

" This volume is the latest addition to the excellent series of special technical works for 
manufacturers and professional and commercial men issued by the well-known publishers of 
The Oil and Colourman's Journal. The volume in every way fully maintains the high standard 
of excellence of the whole series, and deals with the subject of glue making and glue testing in 
a thoroughly exhaustive manner. Chapters are given on the constitution and properties, and 
raw material and manufacture, and of the usesofglue, and in this latter respect it will doubtless 
be information to many readers to learn to what extent glue enters into the manufacture of 
many commercial products not apparently associated with glue. Exhaustive chapters on the 
processes and methods of glue testing, and on its commercial aspects, complete this useful and 
most carefully prepared volume."— Carrta^g Builders' Journal. 

TECHNOLOGY OF PETROLEUM : Oil Fields of the 

World — Their History, Geography and Geology — Annual Production 
and Development — Oil-well Drilling — ^Transport. By Henry Neu- 
BERGER and Henry Noalhat. Translated from the French by J. G. 
McIntosh. 350 pp. 153 Illustrations. 26 Plates. Royal 8vo. 1901. Price 
21s. ; India and Colonies, 22s. ; Other Countries, 2ds. 6d. ; strictly net. 

Contents. 

Part I., Study of (the Petroliferous Strata— Chapters I., Petroleum— Definition.— II., 
The Genesis or Origin of Petroleum. — III., The Oil Fields of Galicia, their History. — IV., 
Physical Geography and Geology of the Galician Oil Fields.— V., Practical Notes on Galician 
Land Law — Economic Hints on Working, etc. — VI., Roumania — History, Geography, Geology. 
— ^VII., Petroleum in Russia — History. — VIII., Russian Petroleum (conf««««d)-— Geography and 
Geology of the Caucasian Oil Fields. — IX., Russian Petroleum {continued).— X.,The Secondary 
Oil Fields of Europe, Northern Germany, Alsace, Italy, etc.— XL, Petroleum in France. — ^XII., 
Petroleum in Asia — ^Transcaspian and Turkestan Territory— Turkestan — Persia— British 
India and Burmah — British Burmah or Lower Burmah — China — Chinese Thibet — Japan, 
Formosa and Saghalien.— XIII., Petroleum in Oceania— Sumatra, Java, Borneo— Isle of 
Timor — Philippine Isles— New Zealand.— XIV., The United States of America — History. — 
XV., Physical Geology and Geography of the United States Oil Fields.— XVI., Canadian and 
other North American Oil Fields.— XVII., Economic Data of Work in North America.— 
XVIII., Petroleum in the West Indies and South America.— XIX., Petroleum in the French 
Colonies. 



10 

Part II., Excavations. — Chapter XX., Hand Excavation or Hand Digging of Oil Wells. 

Part III., Methods of Borinff. — Chapters XXL, Methods of Oil-well Drilling or Boring. 
—XXII., Boring Oil Wells with the Rope.— XXIII., Drilling with Rigid Rods and a Free-fall- 
Fabian System.— XXIV., Free-fall Drilling by Steam Power.— XXV., Oil-well Drilling by the 
Canadian System.— XXVI., Drilling Oil Wells on the Combined System.— XXVII., Com- 
parison between the Combined Fauck System and the Canadian. — XaVIII., The American 
System of Drilling with the Rope. — XXIX., Hydraulic Boring with the Drill by Hand and 
Steam Power.— XXX., Rotary Drilling of Oil Wells, Bits, Steel-crowned Tools, Diamond 
Tools — Hand Power and Steam Power — Hydraulic Sand-pumping. — XXXL, Improvements 
in and different Systems of Drilling Oil Wells. 

Part IV., Accidents.— Chapters XXXII., Boring Accidents — Methods of preventing them 
— Methods of remedying them. — XXXIII., Explosives and the use of the "Torpedo" Leviga- 
tion. — XXXIV., Storing and Transport of Petroleum. — XXXV., General Advice — Prospecting, 
Management and carrying on of Petroleum Boring Operations. 

Part v.. General Data. — Customary Formuiie. — Memento. Practical Part. General 
Data bearing on Petroleum. — Glossary of Technical Terms used in the Petroleum Industry. — 
Copious Index. 

A DICTIONARY OF CHEMICALS AND RAW PRO- 
DUCTS USED IN THE MANUFACTURE OF 
PAINTS, COLOURS, VARNISHES AND ALLIED 
PREPARATIONS. By George H. Hurst, F.C.S. Demy 
8vo. 380 pp. 1901. Price 7s. 6d. ; India and Colonies, 8s.; Other 
Countries, 8s. 6d. ; strictly net. 

Contents. 

The names of the Chemicals and Raw Products are arranged in alphabetical order, and 
the description of each varies in length from half to eight pages. The following are some of 
the articles described and explained : Acetates — Acetic Acid — Acidimetry — Alcohol — Alum — 
Ammonia — Amber — Animi — Arsenic — Beeswax — Benzol — Bichromates of Potash and Soda — 
Bleaching Powder — Bone Black — Boric Acid — Brunswick Green^<}admium Yellow— Car- 
bonates — Carmine — Camauba Wax — Caustic Potash and Soda — Chrome Colours — Clay — Coal 
Tar Colours — Copal — Dammar — Drying Oils — Emerald Green — Gamboge — Glue — Glycerine — 
Gums — Gypsum — Indian Red — Japanese Lacquer — Lac — Lakes — Lamp Black — Lead Com- 
pounds — Lmseed Oil — Magnesia — Manganese Compounds — Mica — Nitric Acid— Ochres — 
Orange Lead — Orr's White — Paraffin — Prussian Blue — Rosin Oil — Sepia — Sienna — Smalts — 
Sodium Carbonate — Sublimed White Lead — Sulphuric Acid — Terra Verte — ^Testin^ Pigments 
— Turpentine — Ultramarine — Umbers — Vermilionettes — White Lead — Whiting — Ztnc Com- 
pounds. — Appendix : Comparison of Baum6 Hydrometer and Specific Gravity for Liquids 
Lighter than Water — Hydrometer Table for Liquids Heavier than Water — Comparison of 
Temperature Degrees — Tables for Converting French Metric Weights and Measures into 
English — Table of the Elements — etc., etc. — Copious Index. 

Press Opinions. 

" This treatise will be welcomed by those interested in this industry who have not secured 
the full advantage of a course of scientific training." — Chemical Trade Journal. 

*' In concise and lucid terms almost every ingredient used in paint and colour manufacture 
is described, together with the methods of testing their intrinsic and chemical value." — 
Pontefract Express. 

" Such a book of reference for paint, colour and varnish manufacturers has long been 
needed, and in Mr. Hurst the publishers have secured a compiler who is not only a well-known 
authority and expert, but who has the gift of communicating his knowledge in a concise and 
lucid form." — Manchester Courier. 

PURE AIR, OZONE AND WATER. A Practical Treatise 

of their Utilisation and Value in Oil, Grease, Soap, Paint, Glue and 
other Industries. By W. B. Cowell. Twelve Illustrations. 1900. 
Price 5s. ; India and Colonies, 5s. 6d. ; Other Countries, 6s. ; strictly net. 

Contents. 

Chapters I., Atmospheric Air; Lifting of Liquids; Suction Process; Preparing Blown Oils; 
Preparing Siccative Drying Oils. — II., Compressed Air; Whitewash. — III., Liquid Air; Retro- 
cession. — IV., Purification of Water; Water Hardness. — V., Fleshings and Bones. — VI., Ozon- 
ised Air in the Bleaching and Deodorising of Fats, Glues, etc. ; Bleaching Textile Fibres. — 
Appendix: Air and Gases; Pressure of Air at Various Temperatures ; Fuel; Table of Com- 
bustibles; Saving of Fuel by Heating Feed Water; Table of Solubilities of Scale Making 
Minerals; British Thermal Units Tables; Volume of the Flow of Steam into the Atmosphere; 
Temperature of Steam. — Index. 

Press Opinions. 

" This is a valuable work in little space. ... In arrangement it is a commendable work, 
and its value is increased by the index which brings the little volume to a close.'* — Newcastle 
Daily Journal. 

"The book is written solely for manufacturers, who, without doubt, will find it exceedingly 
practical and useful. The volume contains an' appendix wherein is given a great many tables, 
etc., which'manufacturers in the trades referred to will find of inestimable valu» " — Rtyjj-khum 
Times. 



11 

THE MANUFACTURE OF MINERAL AND LAKE 

PIGMENTS. Containing Directions for the Manufacture 
of all Artificial, Artists and Painters' Colours, Enamel, Soot and Me- 
tallic Pigments. A Text-book for Manufacturers, Merchants, Artists 
and Painters. By Dr. Josef Bersch. Translated from the Second 
Revised Edition by Arthur C. Wright, M.A. (Oxon.), B.Sc. (Lond.), 
formerly Assistant Lecturer and Demonstrator in Chemistry at the 
Yorkshire College, Leeds. Forty-three Illustrations. 476 pp., demy 
8vo. 190L Price 12s. 6d. ; India and Colonies, 13s. 6d. ; Other 
Countries, 15s. ; strictly net. 

Contents. 

Chapters I., Introduction. — II., Physico-chemical Behaviour of Pigments. — III., Raw 
Materials Employed in the Manufacture of Pigments. — IV., Assistant Materials. — V., Metallic 
Compounds. — VI., The Manufacture of Mineral Pigments. — VII., The Manufacture of White 
Lead.— VIII., Enamel White.— IX.. Washing Apparatus.— X., Zinc White.— XI., Yellow 
Mineral Pigments. — XII., Chrome Yellow. — XIII., Lead Oxide Pigments. — XIV., Other 
Yellow Pigments.— XV., Mosab Gold.— XVI., Red Mineral Pigments.— XVII., The Manu- 
facture of Vermilion. — XVIII., Antimony Vermilion. — XIX., Ferric Oxide Pigments. — XX., 
Other Red Mineral Pigments. — XXI., Purple of Cassius. — XXII., Blue Mineral Pigments. — 
XXIII., Ultramarine.— aXI v.. Manufacture of Ultramarine. — XXV., Blue Copper Pigments. 
—XXVI., Blue Cobalt Pigments.- XXVII., Smalts.— XXVIII., Green Mineral Pigments.— 
XXIX., Emerald Green.— XXX., Verdigris.- XXXI., Chromium Oxide.— XXXII., Other 
Green Chromium Pigments. — XXXIII., Green Cobalt Pigments. — XXXI V^ Green Man- 
ganese Pigments. — XXXV., Compounded Green Pigments. — XXXVI., Violet Mineral Pig- 
ments. — XXXVII., Brown Mineral Pigments. — XXXVIII., Brown Decomposition Products. — 
XXXIX., Black Pigments. — XL., Manufacture of Soot Pigments. — XLI., Manufacture of 
Lamp Black. — XLII., The Manufacture of Soot Black without Chambers. — XLIII., Indian 
Ink. — XLI v.. Enamel Colours. — XLV., Metallic Pigments. — XLVI., Bronze Pigments — 
XLVIL, Vegetable Bronze Pigments. 

PiGBENTS OP Organic Origin. — Chapters XLVIII., Lakes.- XLIX., Yellow Lakes. — L., 
Red Lakes. — LI., Manuhicture of Carmine. — LI I., The Colouring Matter of Lac. — LI 1 1., Saf- 
flower or Carthamine Red. — LIV., Madder and its Colouring Matters. — LV., Madder Lakes. — 
LVI., Manjit (Indian Madder). — LVII., Lichen Colouring Matters. — LVIII., Red Wood Lakes. 
— LIX., The Colouring Matters of Sandal Wood and Other Dye Woods. — LX., Blue Lakes. — 
LXI., Indigo Carmine. — LXII., The Colouring Matter of Log Wood. — LXIII., Green Lakes. — 
LXIV., Brown Organic Pigments.— LXV., Sap Colours.— LX VI., Water Colours.— LXVI I., 
Crayons. — LXVI 1 1., Confectionery Colours. — LXIX., The Preparation of Pigments for 
Painting. — LXX., The Examination of Pigments. — LXXI., Examination of Lakes. — LXXII., 
The Testing of Dye-Woods.— LXXIII., The Design of a Colour Works.— LXXIV.— Commercial 
Names of Pigments. — Appendix: Conversion of Metric to English Weights and Measures. — 
Centigrade and Fahrenheit Thermometer Scales. — Index. 

BONE PRODUCTS AND MANURES : An Account of the 

most recent Improvements in the Manufacture of Fat, Glue, Animal 
Charcoal, Size, Gelatine and Manures. By Thomas Lambert, Techni- 
cal and Consulting Chemist. Illustrated by Twenty-one Plans and 
Diagrams. 162 pp., demy 8vo. 1901. Price 7s. 6d. ; India and 
Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 

Contents. 

Chapters I., Chemical Composition of Bones — Arrangement of Factory — Crushing of Bones 
— ^Treatment with Benzene — Benzene in Crude Fat — ^Analyses of Clarified Fats — Mechanical 
Cleansing of Bones — Animal Charcoal — Tar and Ammoniacal Liquor, Char and Gases, from 
good qusuity Bones — Method of Retorting the Bones — Analyses of Chars — " Spent " Chars — 
Cooling of Tar and Ammoniacal Vapours — Value of Nitrogen for Cyanide of Potash— Bone 
Oil — ^Marrow Bones^-Composition of Marrow Fat — Premier Juice — Buttons. — II., Properties 
of Glue — Glutin and Chondrin — Skin Glue — Liming of Skins — Washing — Boiling of Skins — 
Clarification of Glue Liquors — ^Acid Steeping of Bones — Water System of Boilmg Bones-*- 
Steam Method of Treating Bones — Nitrogen in the Treated Bones— -Glue-Boiling and Clarify- 
ing-House — Plan showing Arrangement or Clarifying Vats — Plan showing Position of Evapora- 
tors-— Description of Evaporators — Sulphurous Acid Generator — Clarification of Liquors — 
Section of Drying-House — Specification of a Glue — Size — Uses and Preparation and Composi- 
tion of Size — Concentrated Size. — III., Properties of Gelatine — Preparation of Skin Gelatine 
— ^Washing — Bleaching — Boiling — Clarification — Evaporation — Drying — Bone Gelatine — Se- 
lecting Bones— Crushing — Diss<Mving — Bleaching — Boiling — Properties of Glutin and Chondrin 
— ^Testing of Glues and Gelatines. — IV., The Uses of Glue, Gelatine and Size in Various 
Trades — Soluble and Liquid Glues — Steam and Waterproof Glues. — V., Manures — Importation 
of PoodStuflis — Soils— Germination — Plant Life. — VI., Natural Manures — Water and Nitrogen 
in Farmyard Manure — Full Analysis of Farmyard Manure — Action on Crops — Water-Closet 



12 

System — Sewage Manure — Green Manures. — VII., Artificial Manures — Bones — Boiled and 
Steamed Bones— Mineral Phosphates — English Coprolites — French and Spanish Phosphorites 
— German and Belgian Phosphates — Basic Slag— Guanos Proper — Guano Phosphates.— VIII., 
Mineral Manures — Common Salt — Potash Salts — Calcareous Manures — Prepared Nitrogenous 
Manures — Ammoniacal Compounds — Sodium Nitrate — Potassium Nitrate — Organic Nitro- 
genous Matters — Shoddy — Hoofs and Horns — Leather Waste — Dried Meat — Dried Blood — 
Superphosphates— Composition — Manufactuie — Section of Manure-Sh^ — First and Ground 
Floor Plans of Manure-Shed — Quality of Acid Used — Mixings — Special Manures — Potato 
Manure — Dissolved Bones — Dissolved Bone Compound — Enriched Peruvian Guano — Special 
Manure for Garden Stufl^, etc. — Special Manure for Grass Lands — Special Tobacco Manures 
— Sugar-Cane Manure — Compounding of Manures — Valuation of Manures. — IX., Analyses of 
Raw and Finished Products — Common Raw Bones — Degreased Bones— Crude Fat — Refined 
Fat — Degelatinised Bones — Animal Charcoal — Bone Superphosphates — Guanos — Dried Animal 
Products — Potash Compounds — Sulphate of Ammonia — Extraction in Vacuo — Description of a 
Vacuum Pan — French and British Gelatines compared. — Index. 

Press Opinion. 

" We can with confidence recommend the perusal of the book to all persons interested in 
the manufacture of artificial manures, and also to the large number of farmers and others who 
are desirous of working their holdings on the most up-to-date methods, and obtaining the best 
possible results, which scientific research has placed within their reach." — Wigan Observer. 

ANALYSIS OF RESINS AND BALSAMS. Demy 8vo. 

340 pp. 1901. Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 
8s. 6d. ; strictly net. 

Contents. 

Part I., Definition of Resins in General — Definition of Balsams, and especially the Gum 
Resins — External and Superficial Characteristics of Resinous Bodies — Distinction between 
Resinous Bodies and Fats and Oils — Origin, Occurrence and Collection of Resinous Sub- 
stances — Classification — Chemical Constituents of Resinous Substances — Resinols — Resinot 
Annols — Behaviour of Resin Constituents towards the Cholesterine Reactions — Uses and 
Identification of Resins — Melting-point — Solvents — Acid Value — Saponification Value — Resin 
Value — Ester and Ether Values— Acetyl and Corbonyl Value — Methyl Value — Resin Acid — 
Systematic R^sum^ of the Performance of the Acid and Saponification Value Tests. 

Part II., Balsams — Introduction — Definitions — Canada Balsam — Copaiba Balsam — Angos- 
tura Copaiba Balsam — Babia Copaiba Balsam — Carthaj^ena Copaiba Balsam — Maracaibo 
Copaiba Balsam — Maturin Copaiba Balsam — Gurjum Copaiba Balsam — Para Copaiba Balsam 
— Surinam Copaiba Balsam — West African Copaiba Balsam — Mecca Balsam — Peruvian 
Balsam — Tolu Balsam — Acaroid Resin — Amine — Amber — African and West Indian Kino- 
Bengal Kino — Labdanum — Mastic — Pine Resin — Sandarach — Scammonium — Shellac — Storax 
— Adulteration of Styrax Liquidus Crudus — Purified Storax — Styrax Crudus Colatus — Taca- 
mahac — Thapsia Resin — Turpentine — Chios Turpentine — Strassburg Turpentine — Turpeth 
Turpentine. Qum Resins — Ammoniacum — Bdellium — Euphorbium — Galbanum — Gamboge 
— Lactucarium — Myrrh — Opopanax — Sagapenum — Olibanum or Incense — Acaroid Resin — 
Amber — Thapsia Resin. — Index. 

MANUFACTURE OP PAINT. A Practical Handbook for 

Paint Manufacturers, Merchants and Painters. By J. Cruickshank 
Smith, B.Sc. Demy 8vo. 1901. 200 pp. 60 Illustrations and 1 Large 
Diagram. Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 
8s. 6d. ; strictly net. 

Contents. 

Part I., Chapters I., Preparation of Raw Material. — II., Storing of Raw Material. — III., 
Testing and Valuation of Raw Material — Paint Plant and Machinery. 

Part II., Chapters V., The Grinding of White Lead.— VI., Grinding of White Zinc— VII., 
Grinding of other White Pigments.— VIII., Grinding of Oxide Paints.— IX., Grinding of Stain- 
ing Colours.— X., Grinding of Black Paints.— XI., Grinding of Chemical Colours— Yellows. — 
XII., Grinding of Chemical Colours— Blues. — XIII., Grindmg Greens. — XIV., Grinding Reds. 
— XV., Grinding Lakes. — XVI., Grinding Colours in Water. — ^XVII., Grinding Colours in 
Turpentine. 

Part III., Chapters XVIII., The Uses of Paint.— XIX., Testing and Matching Paints.— 
XX., Economic Considerations. — Index. 

THE CHEMISTRY OP PIGMENTS. By Ernest J. Parry, 

^ B.Sc, F.I.C., F.C.S., and J. H. Coste, F.I.C, F.C.S. [In the press, 

" Contents. 

Chapters I., Introductory— Composition of White Light— Theory of Colour, etc.— II., The 
Application of Pigments— Artistic, Decorative, Protective Methods of Applying Pigments. — 
III., White Pigments. — IV., Inorganic Coloured Pigments.— V., Organic Pigments. 



13 

NOTES ON LEAD ORES : Their Distribution and Properties. 
By Jas. Fairie, F.G.S. Crown 8vo. 1901. 64 pages. Price 28. 6d. ; 
Abroad, 3s. ; strictly net. 

Contents. 

Chapters I., Definitions — Properties-^Occurrence. — fl., Galena — Johnstonite — Cerussite — 
Ceruse (White Lead) — Minium — Red Lead. — III,, Pyromorphite — Mimetene — Hediphane — 
Crocoise — Wulfenitc. — Vanadinite — IV., BleiglSltte — Anglesite — Caledonite — Linarite — Lanark- 
ite — Leadhillite — Susannite — Clausthalite — Cotunnite. — V., Mendipite — Matlockite — Crom- 
fordite — Nagyagite — Altaite — Melanochroite — Vauguelinite — Scheeletine. — VI., Plattncrite — 
Tilkcrodite — Raphanosmite — Deckenite — Descloezite — Dufrenaysite — Bleinierite — Moffrasite 
— Geocronite — Kilbrechenite — Schulzite — Boulangcrite — Heteromorphite — Meneghinite — 
Jamesonite — Plagionite — Zinkenite. — VII., Kobelnte — Boumonite — Selenkupferblei — Nus- 
sierito — Percylite — Wolchitc — Polysphracrite— Micsite. — Index. 



THE RISKS AND DANGERS OF VARIOUS OCCUPA- 
TIONS AND THEIR PREVENTION. By Leonard 

A. Parry, M.D., B.S. (Lond.). 196 pp., demy 8vo. 1900. Price 7s. 6d. ; 
India and Colonies, 8s. ; Other Countries, 88. 6d. ; strictly net. 

Contents. 

Chapters I., Occupations which are Accompanied by the Generation and Scattering of 
Abnormal Quantities of Dust. — II., Trades in which there is Danger of Metallic Poisoning. — 
III., Certain Chemical Trades. — IV., Some Miscellaneous Occupations. — V., Trades in which 
Various Poisonous Vapours are Inhaled. — ^VI., General Hygienic Considerations. — Index. 

This book contains valuable information for the following trades — Aerated Water Manu- 
facture, Alkali Manufacture, Aniline Manufacture, Barometer Making, Brass Founders, Bromine 
Manufacture, Bronze Moulders, Brush Making, Builders, Cabinet Makers, Calico Printing, 
Chloride of Lime Manufacture, Coal Miners, Cocoa-nut Fibre Making, Colour Grinders, 
Copper Miners, Cotton Goods Manufacture, Cotton Yarn Dyeing, Cutlery Trades, Dry Clean- 
ing, Electricity Generating, Electroplaters, Explosives Manufacture, File Making, Flint 
Milling, Floor Cloth Makers, Furriers, Fustian Clothing Making, Galvanised Iron Manufacture, 
Gassing Process, Gilders, Glass Making, Glass Paper Making, Glass Polishing and Cutting, 
Grinding Processes, Gunpowder Manufacturing, Gutta-percha Manufacture, Hat Makers, 
Hemp Manufacture, Horn Goods Making, Horse-hair Making, Hydrochloric Acid Manufacture, 
India-rubber Manufacture, Iodine Manufacture, Ivory Goods Making, Jewellers, Jute Manu- 
facture, Knife Grinders, Knife Handle Makers, Lace Makers, Lacquering, Lead Melters, Lead 
Miners, Leather Making, Linen Manufacture. Linoleum Making, Lithographic Printing and 
Bronzing, Lithographing, Masons, Match Manufacture, Melanite Making, Mirror Making, 
Needle Grinders, Needle Making, Nitro-benzole Making, Nitro-glycerine Making, Paint 
Makers, Paper Making, Philosophical Instrument Makers, Photographers, Picric Acid Making, 
Portland Cement Making, Pottery Manufacture, Printers, Quicksilver Mining, Rag Pickers, 
Razor Grinders, Red Lead Making, Rope Making, Sand Paper Making, Saw Gnnders, Scissors 
Grinders, Shoddy Manufacture, Shot Making, Silk Making, Silver Mining, Skinners, Slag, Wood 
Manufacture, Steel Makers, Steel Pen Making, Stereotypers, Stone Masons, Straw Hat Makers, 
Sulphuric Acid Manufacture, Sweeps, Table-knife Grinders, Tanners, Telegraphists, Textile 
Industries, Tin Miners, Turners, Type Founders, Umbrella Makers, Wall Paper Making, 
White Lead Making, Wood Working, Woollen Manufacture, Wool Sorters, Zinc Oxide 
Manufacture, Zmc Working, etc., etc. 

Press Opinions. 

"The language used is quite simple, and can be understood by any intelligent person en- 
gaged in the trades dealt with." — The Clarion. 

" This is an appalling book. It shows that there is scarcely a trade or occupation that has 
not a risk or a danger attached to it." — Local Government Journal. 

" Dr. Parry has not only pointed out the ' risks and dangers of various occupations * ; he has 
suggested means for their prevention. The work is primarily a practical one." — Colliery 
Manager. 

"This is a most useful book which should be in the hands of all employers of labour, 
foremen, and intelligent workmen, and is one of great utility to sanitary inspectors, and even 
on occasion to medical men." — Health. 

"The writer has succeeded in collecting a large amount of information, and though one 
could wish he had presented it in a rather more attractive style, he has certainly condensed it 
into a venr small space." — Physician and Surgeon. 

" The little book before us is one which will be found exceedingly useful to manufacturers 
and even factory inspectors. . . . No attempt is made to show how diseases when originated 
are to be curedf, but, acting on the sound principle that prevention is better than cure, means 
are stated how to avoid the harm." — Bristol Mercury. 

" The author has. endeavoured to treat the question in simple rather than in technical lan- 
guage, and he has lucidly catalogued the most dangerous trades and their symptoms, and in 
each case specified the best methods of dealing with them. . . . To those for whom the volume 
is specially designed. Dr. Parry's treatise should be a useful handbook." — Sheffield Independent. 



14 

** A verv useful manual for emplovere of labour, foremen, intelligent workmen, and, in spite 
of the author's modesty, for medical men. We have the peculiar risks and dangers of all the 
dangerous trades careJrully described ; the mode of action of various chemicals, etc., used in 
different industries given, with full directions how to minimise unavoidable risks." — Leeds 
Mercury. 

" Most of the trades in the country are alluded to, and upon those that are dangerous the 
necessary attention is bestowed, and means are recommended whereby danger may be pre- 
vented or lessened. The author has evidently studied his subject with care, and has made full 
use of the experience of others who have had a larger insight into the industries of the country." 
—British Medical Journal. 

"The work is well written and printed, and its verbiage such as to be comprehensible to the 
workman no less than to the master. The careful and general perusal of a work of this nature 
cannot but be attended by beneficial results of a far-reaching nature, and we therefore heartily 
recommend the book to our readers. Medical Officers of Health and Sanitary Inspectors 
especially should find the work of great interest." — Sanitary Record. 

" It is written in simple language, and its instructions can be easily followed. . . . There 
are some employers, at any rate, who are more ignorant of, than indifferent to, the slow murder 
of their workpeople, and if the facts so succinctly set forth in this book were brought to their 
notice, and if the Trade Unions made it their business to insist on the observance of the better 
conditions Dr. Parry described* much might be done to lessen the workman's peril." — Weekly 
Times and Echo. 



PRACTICAL X RAY WORK. By Frank T. Addyman, 

B.Sc. (Lond.), F.I.C., Member of the Roentgen Society of London; 
Radiographer to St. George's Hospital ; Demonstrator of Physics and 
Chemistry, and Teacher of Radiography in St. George's Hospital 
Medical School. Demy 8vo. 12 Plates from Photographs of X Ray 
Work. 52 Illustrations. 200 pp. 1901. Price 10s. 6d. ; India and 
Colonies, lis.; Other Countries, 12s.; strictly net. 

Contents. 

Part 1., Historical — Chapters I., Introduction. — II., Work leading up to the Discovery of 
the X Rays. — III., The Discovery. 

Part II., Apparatus and its Management — Chapters I., Electrical Terms. — II., Sources 
of Electricity. — III., Induction Coils. — IV., Electrostatic Machines. — ^V., Tubes. — VI., Air 
Pumps. — VII., Tube Holders and Stereoscopic Apparatus. — VIII., Fluorescent Screens. 

Part III., Practical X Ray Worlc — Chapters I., Installations. — II., Radioscopy. — III., 
Radiography. — IV., X Rays in Dentistry. — V., X Rays in Chemistry. — VI., X Rays in War. — 
Index. 

List Of Plates. 

Frontispiece — Congenital Dislocation of Hip-Joint. — I., Needle in Finger. — II., Needle in 
Foot. — III., Revolver Bullet in Calf and Leg. — IV., A Method of Localisation. — V., Stellate 
Fracture of Patella showing shadow of "Strapping". — VI., Sarcoma. — VII., Six-weeks'-old 
Injury to Elbow showing new Growth of Bone. — VIII., Old Fracture of Tibia and Fibula 
badly set. — IX., Heart Shadow. — X., Fractured Femur showing Grain of Splint. — XI., Bar- 
relPs Method of Localisation. 



DRYING BY MEANS OP AIR AND STEAM. Explana- 
tions, Formulae, and Tables for Use in Practice. Translated from the 
German of E. Hausbrand. Two Diagrams and Thirteen Tables. Demy 
8vo. 1901. 72 pp. Price 5s.; India and Colonies, 5s. 6d. ; Other 
Countries, 6s. ; strictly net. 

Contents. 

Preface. — British and Metric Systems Compared — Centigrade and Fahr. Thermometers. — 
Chapters I.,' Introduction. — II., Estimation of the Maximum Weight of Saturated Aqueous 
Vapour which can be contained m 1 kilo, of Air at Different Pressure and Tempera- 
tures. — III., Calculation of the Necessary Weight and Volume of Air, and of the Least 
Expenditure of Heat, per Drying Apparatus with Heated Air, at the Atmospheric Pressure : 
A, With the Assumption that the Air is Completely Saturated with Vapour both before Entry 
and after Exit from the Apparatus. — B, When the Atmospheric Air is Completely Saturated 
before entry^ but at its exit is only 3, i or J Saturated. — C, When the Atmospheric Air is not 
Saturated with Moisture before Entering the Drying Apparatus. — IV., Drying Apparatus, in 
which, in the Drying Chamber, a Pressure is Artificially Created, Higher or Lower than that 
of the Atmosphere. — V., Drying by Means of Superheated Steam, without Air. — VI., Heating 
Surface, Velocity of the Air Current, Dimensions of the Drying Room, Surface of the Drying 
Material, Losses of Heat. — Index. 



15 

Leather Trades. 

THE LEATHER WORKER'S MANUAL. Being a Com- 
pendium of Practical Recipes and Working Formulae for Curriers, 
Bootmakers, Leather Dressers, Blacking Manufacturers, Saddlers, 
Fancy leather Workers, and all Persons engaged in the Manipulation 
of Leather. By H. C. Standage. 165 pp. 1900. Price 7s. 6d. ; 
India and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 

Contents. 

Chapters I., Blackings, Polishes, Glosses, Dressings, Renovators, etc., for Boot suid Shoe 
Leather. — II., Harness Blackings, Dressings, Greases, Compositions, Soaps, and Boot-top 
Powders and Liquids, etc., etc. — III., Leather Grinders' Sundries. — IV., Currier's Seasonings, 
Blacking Compounds, Dressings, Finishes, Glosses, etc. — V., Dyes and Stains for Leather. — 
VI., Miscellaneous Information. — ^VII., Chrome Tannage. — Index. 

Press Opinions. 

" The book being absolutely unique, is likely to be of exceptional value to all whom it con« 
cerns, as it meets a long-felt want." — Birmingham Gazette. 

** This is a valuable collection of practical receipts and working formulae for the use of those 
engaged in the manipulation of leather. We have no hesitation in recommending it as one of 
the best books of its kind, an opinion which will be endorsed by those to whom it appeals." — 
Liverpool Mercury. 

" We think we may venture to state, so far as the opinion of the leather trade under the 
Southern Cross is concerned, that it will be one of approval. As practical men, having a long 
and wide experience of the leather trade in Australia, we are certain that there are many 
tanners and curriers carrying on business in remote townships of the colonies to whom such a 
manual of practical recipes will be invaluable. . . . This manual is not a mere collection of r^ 
cipes for the various purposes to which they may be applied, but it is also replete with instruc- 
tions concerning the nature of the materials recommended to be used in making up the recipes. 
. . . We think every intelligent leather man should avail himself of the manual. It is un- 
doubtedly a valuable contribution to the technology of the leather trade." — A ustralian Leather 
Journal and Boot and Shoe Recorder. 

PRACTICAL TREATISE ON THE LEATHER IN- 
DUSTRY. By A. M. Villon. A Translation of Villon's 

'* Traite Pratique dc la Fabrication des cuirs et du Travail des Peaux ". 
By Frank T. Addyman, B.Sc. (Lond.), F.LC, F.C.S. ; and Corrected 
by an Eminent Member of the Trade. 500 pp., royal 8vo. 190L 123 
Illustrations. Price 21s. ; India and Colonies, 22s. ; Other Countries, 
23s. 6d. ; strictly net. 

Contents. 

Preface — Translator's Preface — List of Illustrations. 

Part I., Materials used in Tanning'— Chapter I., Skins: I., Skin and its Structure; II., 
Skins used in Tanning; III., Various Skins and their Uses — Chapter II., Tannin and Tanning 
Substances: I., Tannin; II., Barks (Oak); III., Barks other than Oak; IV., Tanning 
Woods; v.. Tannin-bearing Leaves; VI., Excrescences; VII., Tan-bearing Fruits; VIII., 
Tan-bearing Roots and Bulbs; IX., Tanning Juices ; X., Tanning Substances used in Various 
Countries; XL, Tannin Extracts; XII., Estimation of Tannin and Tannin Principles. 

Part II., Tanning — Chapter I., The Installation of a Tannary: I., Tan Furnaces; II., 
Chimneys, Boilers, etc.; III., Steam Engines — Chapter II., Grinding and Trituration of 
Tanning Substances: I., Cutting up Bark; II., Grinding Bark; III., The Grinding of Tan 
Woods; IV., Powdering Fruit, Galls and Grains; V., Notes on the Grinding of Bark — Chap> 
ter III., Manufacture of Sole Leather: I., Soaking; II., Sweating and Unhairing; III^ 
Plumping and Colouring; IV., Handling; V., Tanning; VI., Tanning Elephants' Hides; 
VII., Drying; VI 1 1., Striking or Pinning— Chapter IV., Manufacture of Dressing Leather: 
I., Soaking; II., Depilation; III., New Processes for the Depilation of Skins; IV., Tanning; 
v., Cow Hides; VI., Horse Hides; VII., Goat Skins; Manufacture of Split Hides — Chap 
ter v.. On Various Methods of Tanning: I., Mechanical Methods; IL, Physical Methods; 
III., Chemical Methods; IV., Tanning with Extracts — Chapter VI., Quantity and Quality: 
I., Quantity; IL, Net Cost; III., Quality of Leather — Chapter VII., Various Manipulations 
of Tanned Leather: I., Second Tanning; IL, Grease Stains; III., Bleaching Leather; IV., 
Waterproofing Leather; V., Weighting Tanned Leather; VI., Preservation of Leather— 
Chapter VIII., Tanning Various Skins. 

Part III., CurryinjT— Chapter I., Waxed Calf: I., Preparation; IL, Shaving; III., 
Stretching or Slicking ; IV.. Oiling the Grain ; V., Oiling the Flesh Side ; VI., Whitening and 
Graining; VII., Waxing; VIIL, Finishing; IX., Dry Finishing; X., Finishing in Colour; 
XL, Cost— Chapter IL, White Calf: I., Finishing in White— Chapter III., Cow Hide for 
Upper Leathers: I., Black Cow Hide; IL, White Cow Hide; III., Coloured Cow Hide. — 
Chapter IV., Smooth Cow Hide— Chapter V., Black Leather— Chapter VI., Miscellaneous 
Hides: I., Horse; II.. Goat; III., Waxed Goat Skin; IV., Matt Goat Skin— Chapter VII., 
Russia Leather: I., Russia Leather; II. . Artificial Russia Leather. 



16 

Part IV., Enamelled, Hungary and Chamoy Leather, Morocco, Parchment, Furs 
and Artificial Leather — Chapter I., Bnafnelled Leather: L, Varnish Manufacture; II.. 
Application of the Enamel; III., Enamelling in Colour — Chapter II., Hungary Leather: I., 
Preliminary; 11^ Wet Work or Preparation; III., Aluming; IV., Dressing or Loft Work; 
v., Tallowing; VI., Hungary Leather from Various Hides—Chapter III., Tawing: I., Pre- 
paratory Operations; II., Dressing; III., Dyeing Tawed Skins; IV., Rugs— Chapter IV., 
Chamoy Leather — Chapter V., Morocco: I., Preliminary Operations; II., Morocco Tanning; 
III., Mordants used in Morocco Manufacture; IV., Natural Colours used in Morocco 
Dyeing; V., Artificial Colours ; VI. Different Methods of Dyeing; VII., Dyeing with Natural 
Colours; VIII., Dyeing with Aniline Colours; IX., Dyeing with Metallic Salts; X., Leather 
Printing; XI., Finishing Morocco; XII., Shagreen; AlII., Bronzed Leather— Chapter VI., 
Gilding and Silvering: I., Gilding; II., Silvering; III., Nickel and Cobalt — Chapter VII., 
Parchment — Chapter VIII., Furs and Furriery: I., Preliminary Remarks; II., Indigenous 
Furs; III., Foreign Furs from Hot Countries; IV. Foreign Furs from Cold Countries; V., 
Furs from Birds' Skins; VI., Preparation of Furs; VII., Dressing; VIII., Colouring; IX., 
Preparation of Birds' Skins; X., Preservation of Furs<— Chapter IX., Artificial Leather: I., 
Leather made from Scraps; II., Compressed Leather; III., American Cloth; IV., Papier 
M&ch6 ; v.. Linoleum ; VI., Artificial Leather. 

Part v., Leather Testing and the Theory of Tanning— Chapter I., Testing and Analysis 
of Leather: I., Physical Testing of Tanned Leather; IL, Chemical Analysis — Chapter II., 
The Theory of Tanning and the other Operations of the Leather and Skin Industry: I., 
Theory of Soaking; if., Theory of Unhairing; III., Theory of Swelling; IV., Theory of 
Handlmg; V. Theory of Tanning; VI., Theory of the Action of Tannin on the Skin; VII., 
Theory of Hungary Leather Making; VIII., Theory of Tawing; IX., Theory of Chamoy 
Leather Making ; X., Theory of Mineral Tanning. 

Part VI., Uses of Leatner— Chapter I., Machine Belts: I., Manufacture of Belting; II., 
Leather Chain Belts; III., Various Belts, IV., Use of Belts— Chapter II., Boot and Shoe- 
making: I., Boots and Shoes; II., Laces — Chapter III., Saddlery: I., Composition of a 
Saddle; II., Construction of a Saddle— Chapter IV., Harness: I., The Pack Saddle; II., 
Harness — Chapter V., Military Equipment— Chapter VI., Glove Making — Chapter VII., 
Carriage Building — Chapter VIlI., Mechanical Uses. 

Appendix, The World's Commerce in Leather— I., Europe; II., America; III., Asia; 
IV., Africa ; Australasia — Index. 

Press Opinions. 

" The book is well and lucidly written. The writer is evidently a practical man, who also 
has taken the trouble to make himself acquainted with the scientific and technical side of his 
trade. . . . French methods differ largely from our own ; sometimes we think our ways the 
best, but not always. The practical man may pick up many useful hints which may help him 
to improve his methods." — Shoe Manufacturers' Monthly Journal. 

" "This book cannot fail to be of great value to all engaged in the leather trades. . . . The 
British may believe that the French can teach them nothing in the work of leather tanning 
generally, but a comparison of the methods of the two countries will certainly yield a few 
wrinkles which may lead to advantageous results. Only a man understanding the science and 
technique of the trade could have written the book, and it is well done." — Midland Free Press. 

" Gives much useful and interesting information concerning the various processes by which 
the skins of animals are converted into leather. Written by a French Chemist aner five 
years of constant study and application; it shows all that detail of analysis which we are 
accustomed to find in scientists, and which the practical tanner is too much in the habit of 
ignoring, sometimes to his own loss." — Leeds Mercury. 

" Nor can there be much doubt that this expectation will be fully justified by the result. 
Thanks to the conspicuous painstaking with which Mr. Addyman has discharged his duty, and 
the 123 illustrations by which the text is elucidated, the volume can hardly fail to prove a very 
valuable standard work of its class. It can thus be confidently recommended to all who are 
more or less practically interested in the technology of a very important subject." — Leicester 
Post. 

" This is, in every respect, an altogether admirable, practical, clear and lucid treatise on 
the various and numerous branches of the great leather industry, of which it deals in an ex- 
haustive, highly intelligent, workmanlike and scientific manner. . . . It i» a handsome addition 
to every man's knowledge of his trade, whether he be a leading director of a large public com- 
pany, or an industrious employee in the works, wishing to improve his services by the addition 
of his brains to his work." — Shoe and Leather Trader. 

" M. Villon writes as one having a very full knowledge of all branches of the subject, and in 
days when foreign competition has enforced on English manufacturers the importance of no 
longer being content with rule-of-thumb methods which have come down to them from their 
forefathers it certainly should be worth the while of English tanners to see what lessons they 
can learn from French practice, and French practice, we should imagine, could hardly have a 
better exponent than the author of this large volume." — Western Daily Press and Bristol Times. 

'* At a time when all or nearly all our British industries are to a greater or less extent 
hampered by the pressure of continental and American competition, any hints that can be 
obtained as to the methods pursued by competitors must necessarily be of value. . . . That it 
will be of interest and value, not merely to English tanners, but to those associated with many 
kindred industrial branches, goes without saying. ... As a work of reference the volume will 
be extremely useful in the trade, and where leisure affords sufficient opportunity a careful 
perusal and study of it would afford ample reward." — Kettering Guardian. 

"This is a very handsomely got up and elaborate work just issued by this well-known 
technical book-publishing firm. . . . When we say that the work consists of over 500 large 
pages with about 120 illustrations, and almost innumerable tables, it will be seen at once that 



17 

we cannot attempt anything like an exhaustive risumi of its contents, and even if we did the 
details would be of little interest to our general readers, while those who are engaged in the 
leather industry will probably obtain the book for themselves — ^at least they would do well to 
do so. . . . Altogether the ' Treatise ' has evidently been very carefully prepared, and by a man 
who thoroughly knows the subject, and hence it will be a very valuable technical book for 
English firms and workers.' — Walsall Observer. 

Books on Pottery, Bricks, 
Tiles, Glass, etc. 

THE MANUAL OP PRACTICAL POTTING. Revised 

and Enlarged. Third Edition. 200 pp. 1901. Price 17s. 6d.; India 
and Colonies, 18s. 6d. ; Other Countries, 20s. ; strictly net. 

Contents. 

Introduction. The Rise and Progress of the Potter's Art. — Chapters I., Bodies. China 
amd Porcelain Bodies, Parian Bodies, Semi-porcelain and Vitreous Bodies, Mortar Bodies, 
Earthenwares Granite and C.C. Bodies, Miscellaneous Bodies, Sagger and Crucible Clays, 
Coloured Bodies, Jasper Bodies, Coloured Bodies for Mosaic Painting, Encaustic Tile Bodies, 
Body Stains, Coloured Dips. — II., Qlazes. China Glazes, Ironstone Glazes, Earthenware 
Glazes, Glazes without Lead, Miscellaneous Glazes, Coloured Glazes, Majolica Colours. — III., 
Qold and Cold Colours. Gold, Purple of Cassius, Marone and Ruby, Enamel Coloured 
Bases, Enamel Colour Fluxes, Enamel Colours, Mixed Enamel Colours, Antique and Vellum 
Enamel Colours, Underglaze Colours, Underglaze Colour Fluxes, Mixed Under^laze Colours, 
Plow Powders, Oils and Varnishes. — IV., Means and Methods. Reclamation of Waste 
Gold, The Use of Cobalt, Notes on Enamel Colours, Liquid or Bright Gold.— V., Classification 
and Analysis. Classification of Clay V^are, Lord Playfair's Analysis of Clays, The Markets 
of the World, Time and Scale of Firing, Weights of Potter's Material, Decorated Goods 
Count. — VI., Comparative Loss of Weight of Clays. — VII., Ground Felspar Calculations. — 
VIII., The Conversion of Slop Body Recipes into Dry Weight.— IX., The Cost of Prepared 
Earthenware Clay. — X., Forms and Tables. Articles of Apprenticeship, Manufacturer's 
Guide to Stocktaking, Table of Relative Values of Potter's Materials, Hourly Wages Table. 
Workman's Settling Table, Comparative Guide for Earthenware and China Manufacturers in 
the use of Slop Flint and Slop Stone, Foreign Terms applied to Earthenware and China 
Goods, Table for the Conversion of Metrical Weights and Measures on the Continent of South 
America. Index. 

CERAMIC TECHNOLOGY : Being some Aspects of Tech- 
nical Science as Applied to Pottery Manufacture. Edited by Charles 
F. BiNNS. 100 pp. 1897. Price 12s. 6d. ; India and Colonies, 13s. 6d. ; 
Other Countries, 15s. ; strictly net. 

Contents. 

Preface. — Introduction. — Chapters I., The Chemistry of Pottery. — II., Analysis and Syn- 
thesis. — III., Clays and their Components. — IV., The Biscuit Oven. — ^V., Pyrometry. — VI., 
Glazes and their Composition. — VII., Colours and Colour-making. — Index. 

BECIPES FOR FLINT GLASS MAKING. By a British 

Glass Master and Mixer. Sixty Recipes. Being Leaves from the 
Mixing Book of several experts in the Flint Glass Trade, containing 
up-to-date recipes and valuable information as to Crystal, Demi-crystal 
and Coloured Glass in its many varieties. It contains the recipes for 
cheap metal suited to pressing, blowing, etc., as well as the most costly 
crystal and ruby. British manufacturers have kept up the quality of 
this glass from the arrivals of the Venetians to Hungry Hill, Stour- 
bridge, up to the present time. The book also contams remarks as 
to the result of the metal as it left the pots by the respective metal 
mixers, taken from their own memoranda upon the originals. 1900. 
Price for United Kingdom, 10s. 6d. ; Abroad. 15s. ; United States, $4 ; 
strictly net. 

Contents. 

Ruby — Ruby from Copper — Flint for using with the Ruby for Coating — ^A German Metal — 
Cornelian, or Alabaster — Sapphire Blue — Crysophis — Opal — ^Turquoise Blue — Gold Colour — 
Dark Green — Green (common)— Green for Malachite — Blue for Malachite — Black for Mela- 
chite — Black — Common Canary Batch — Canary — ^White Opaque Glass — Sealing-wax Red — 
Flint — Flint Glass (Crystal and Demi) — Achromatic Glass — Paste Glass— White Enamel— 
Firestone — Dead White (for moons)— White Agate— Canary — Canary Enamel — Index. 



18 

COLOURING AND DECORATION OF CERAMIC 
WARE. By Alex. Brongniart. With Notes and Additions 
by Alphonse Salvetat. Translated from the French. 200 pp. 1898. 
Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; 
strictly net. 

Contents. 

The Pastes, Bodies or Ceramic Articles Capable of being Decorated by Vitrifiable Colours 
— ^The Chemical Preparation of Vitrifiable Colours — Composition and Preparation of Vitrifiable 
Colours — The Oxides — Preparation of Oxides — Preparation of Chromates — Preparation of 
other Colours — Composition and Preparation of Fluxes — Muffle Colours — Recipes for Colours 
— Use of Metals — Lustres — Preparation and Application of Colours — Composition of Coloured 
Pastes — Underglaze Colours — Colours in the Glaze — Overglaze Colours — Painting in Vitri- 
fiable Colours — Gilding — Burnishing — Printing — Enlarging and Reducing Gelatine Prints — 
Muffle Kilns for Vitrifiable Colours — Influence of the Material on the Colour — Changes Re- 
sulting from the Actions of the Fire — Alterations Resulting from the Colours — Alterations in 
Firing. 

HOW TO ANALYSE CLAY. Practical Methods for Prac- 
tical Men. By Holden M. Ashby, Professor of Organic Chemistry, 
Harvey Medical College, U.S.A. Twenty Illustrations. 1898. Price 
2s. 6d. ; Abroad, 3s. ; strictly net. 

Contents. 

List of Apparatus — List of Atomic Weights — Use of Balance, and Burette, Sand Bath, and 
Water Bath — Dessicator — Drying Oven — Filtering — Fusion — Determination of Water, Organic 
Matter, Iron, Calcium, Alkalies, Limestone, Silica, Alumina, Magnesium, etc. — Mechanical 
Analysis — Rational Analysis — Standard Solutions — Volumetric Analysis — Standards for Clay 
Analysis — Sampling. 

ARCHITECTURAL POTTERY. Bricks, Tiles, Pipes, Ena- 

melled Terra-cottas, Ordinary and Incrusted Quarries, Stoneware 
Mosaics, Faiences and Architectural Stoneware. By Leon Lepevrb. 
With Five Plates. 950 Illustrations in the Text, and numerous estimates. 
500 pp., royal 8vo. 1900. Translated from the French by K. H. Bird, 
M.A., and W. Moore Binns. Price 15s. ; India and Colonies, 16s. ; 
Other Countries, 17s. 6d. ; strictly net. 

Contents. 

Part I. Plain Undecorated Pottery. — Chapter I., Clays: § 1, Classification, General Geo- 
logical Remarks. — Classification, Origin, Locality ; § 2, General Properties and Composition : 
Physical Properties, Contraction, Analysis, Influence of Varibus Substances on the Properties 
of Clays ; § 3, Working of Clay-Pits— I. Open Pits : Extraction, Transport, Cost— -II. Under- 
ground Pits — Mining Laws. Chapter II., Preparation of the Clav : Weathering, Mixing, 
Cleaning, Crushing and Pulverising— Crushing Cylinders and Mills, Pounding Machines — 
Damping: Damping Machines — Soaking, Shortening, Pugging: Horse and Steam Pug-Mills, 
Rolling Cylinders — Particulars of the A^ve Machines. Chapter III., Bricks : § 1, Manufacture 
— (1) Hand and Machine Moulding. — I. Machines Working by Compression : on Soft Clay, on 
Semi-Firm Clay, on Firm Clay, on Dry Clay. — II. Expression Machines: with Cylindrical Pro- 
pellers, with Screw Propellers — Dies — Cutting-tables — Particulars of the Above Machines — 
General Remarks on the Choice of Machines — Types of Installations — Estimates — Plenishing, 
Hand and Steam Presses, Particulars — (2) Drying, b^ Exposure to Air, Without Shelter, and 
Under Sheds — Drying-rooms in Tiers, Closed Drymg-rooms, in Tunnels, in Galleries — De- 
tailed Estimates of the Various Drying-rooms, Comparison of Prices — ^Transport from 
the Machines to the Drying-rooms, Barrows, Trucks, Plain or with Shelves, Lifts-^3) Firing 
— I. In Clamps — II. In Intermittent Kilns. ^,Open: a, using Wood; b Coal; fr', in Clamps; 
6", Flame — B, Closed: c. Direct Flame; c', Rectangular; c", Round; d, Reverberatory — III. 
Continuous Kilns : C, with Solid Fuel : Round Kiln, Rectangular Kiln, Chimneys (Plans and 
Estimates)— D, With Gas Fuel, Fillard Kiln (Plans and Estimates), Schneider Kiln (Plans and 
Estimates), Water-gas Kiln — Heat Production of the Kilns ; § 2, Dimensions, Shapes, Colours, 
Decoration, and Quality of Bricks — Hollow Bricks, Dimensions and Prices of Bricks, Various 
Shapes, Qualities — ^Various Hollow Bricks, Dimensions, Resistance, Qualities ; § 3, Applications 
— History — ^Asia, Africa, America, Europe : Greek, Roman, Byzantine, Turkish, Romanesque, 
Gothic, Renaissance, Architecture — ^Architecture of the Nineteenth Century: in Germany, 
England, Belgium, Spain, Holland, France, America — Use of Bricks— Walls, Arches, Pavemente, 
Flues, Cornices — Facing with Coloured Bricks — Balustrades. Chapter IV., Tiles: § 1, His- 
tory; § 2, Manufacture— <1) Moulding, by Hand, by Machinery: Preparation of the Clay, Soft 
Paste, Firm Paste, Hard Paste — Preparation of the Slabs, Transformation into Flat Tiles, into 
Jointed Tiles — Screw, Cam and Revolver Presses — Particulars of Tile-presses — (2) Drying — 
Plsmchettes, Shelves, D^ing-barrows and Truck»H3) Firing — Divided Kilns — Installation of 
MechanicsU Tileworks — Estimates ; § 3, Shapes, Dimensions and Uses of the Principal Types 
of Tile— Ancient Tiles: Flat, Round, Roman, Flemish— Modern Tiles— With Vertical Inter- 
rupted Join : Oilardoni's, Martin's ; Hooked, Boulet's Villa ; with Vertical Continuous Join : 
MuUer's, Alsace, Pantile— Foreign Tiles— Special Tiles— Ridge Tiles, Coping Tiles, Border 
Tiles, Frontons, Gutters, Anteflxes, Membron, Angular — Roofing Accessones : Chimney-pots, 



19 

Mitrons, Lanterns, Chimneys — Qualities of Tiles — Black Tiles — Stoneware Tiles — Particulars 
■of Tiles. Chapter V., Pipes: I. Conduit Pipes — Manufacture — Moulding : Horizontal 
Machines, Vertical Machines, Worked by Hand and Steam — Particulars of these Machines 
— Drying — Firing — II. Chimney Flues — ^Ventiducts and " Boisseaux," " Waggons " — Particulars 
of these Products. Chapter VI., Quarries : 1, Plain Quarries of Ordinary Clay ; 2, of Cleaned 
•Clay — Machines, Cutting, Mixing, Polishing — Drying and Firing — Applications — Particulars of 
Quarries. Chapter VIl., Terra-cotta : History — Manufacture — Application : Balustrades, 
■Columns, Pilasters, Capitals, Friezes, Frontons, Medallions, Panels, Rose-windows, Ceilings 
— Appendix : Official Methods of Testing Terra-cottas. 

Part II. Made-up or Decorated Pottery. — Chapter I., General Remarks on the Deco- 
•ration of Pottery : Dips — Glazes : Composition, Colouring, Preparation, Harmony with 
Pastes — Special Processes of Decoration — Enamels, Opaque, Transparent, Colours, Under- 

flaze. Over-glaze — Other Processes : Crackling, Mottled, Flashing, Metallic Iridescence, 
.ustres. Chapter II., Glazed and Enamelled Bricks — History: Glazing — Enamelling — Appli- 
■cations: Ordinary Enamelled Bricks, Glazed Stoneware, Enamelled Stoneware — Enamelled 
Tiles. Chapter III., Decorated Quarries: I. Paving Quarries — 1, Decorated with Dips — 2, 
Stoneware: A, Fired to Stoneware; a, of Slag Base — Applications; 6, of Melting Clay — 
Applications — B, Plain or Incrusted Stoneware; a, of Special Clay (Stoke-on-Trent) — Manu- 
facture — Application — b, of Felspar Base— Colouring, Manufacture, Moulding, Drying, Firing 
— Applications. — II. Facing Quarries — 1, in Faience — /I, of Limestone Paste — B^ of Silicious 
Paste— C, of Felspar Paste — Manufacture, Firing — 2, of Glazed Stoneware — 3, of Porcelain — 
Applications of Facing Quarries. — III. Stove Quarries — Preparation of the Pastes, Moulding, 
Firing, Enamelling, Decoration — Applications — Faiences for Fireplaces. Chapter IV., Archi- 
tectural Decorated Pottery: § 1, Faiences; g 2, Stoneware; § 3, Porcelain. Chapter V., 
Sanitary Pottery : Stoneware Pipes : Manufacture, Firing — ^Applications — Sinks — Applications 
— Urinals, Seats and Pans — Applications — Drinking-fountains, Washstands. Index. 

A TREATISE ON THE CERAMIC INDUSTRIES. A 

Complete Manual for Pottery, Tile and Brick Works. By Bmile 
BouRRY, Ingenieur des Arts et Manufactures. Translated from the 
French by Wilton P. Rix, Examiner in Pottery and Porcelain to the 
City and Guilds of London Technical Institute, Pottery Instructor to 
the Hanley School Board. Royal 8vo. 1901. Over 700 pp. Price 
21s. ; India and Colonies, 22s. ; Other Countries, 2ds. 6d. ; strictly net. 

Contents. 

Part I., General Pottery Methods. Chapters I., Definition and History. Definitions 
:and Classification of Ceramic Products — Historic Summary of the Ceramic Art. — II., Raw 
Materials of Bodies. Clays : Pure Clay and Natural Clays — Various Raw Materials : Analogous 
to Clay — Agglomerative and Agglutinative — Opening — Fusible — Refractory — Trials of Raw 
Materials. — III., Plastic Bodies. Properties and Composition — Preparation of Raw Materials : 
Disaggregation — Purification — Preparation of Bodies : By Plastic Method — By Dry Method — 
By Liquid Method. — IV., Formation. Processes of Formation : Throwing — Expression — 
Moulding by Hand, on the Jolley, by Compression, by Slip Casting — Slapping — Slipping. — V., 
Drying. Drying of Bodies — Processes of Drying : By Evaporation — By Aeration — By 
Heating — By Ventilation — By Absorption. — VI., Glazes. Composition and Properties — Raw 
Materials — Manufacture and Application. — VII., Firing. Properties of the Bodies and Glazes 
<lurtng Firing — Description of the Kilns — Working of the Kilns. — VIII., Decoration. Colouring 
Materials — Processes of Decoration. 

Part II., Special Pottery Methods. Chapters IX., Terra Cottas. Classification: 
Plain Ordinary, Hollow, Ornamental, Vitrified, and Light Bricks — Ordinary and Black Tiles — 
Paving Tiles — Pipes — ^Architectural Terra Cottas — Vases, Statues and Decorative Objects — 
Common Pottery — Pottery for Water and Filters — ^Tobacco Pipes — Lustre Ware — Propjerties 
And Tests for Terra Cottas. — X., Fireclay Goods. Classification: Argillaceous, Aluminous, 
Carboniferous, Silicious and Basic Fireclay Goods — Fireclay Mortar (Pug) — Tests for Fireclay 
Goods. — XL, Faiences. Varnished Faiences — Enamelled Faiences — Silicious Faiences — Pipe- 
clay Faiences — Pebble Work — Feldspathic Faiences — Composition, Processes of Manufacture 
and General Arrangements of Faience Potteries. — XII., Stoneware. Stoneware Properly So- 
called: Paving Tiles— Pipes — Sanitary Ware — Stoneware for Food Purposes and Chemical 
Productions — Architectural Stoneware — Vases, Statues and other Decorative Objects — Pine 
Stoneware. — XIII., Porcelain. Hard Porcelain for Table Ware and Decoration, for the Fire, 
for Electrical Conduits, for Mechanical Purposes ; Architectural Porcelain, and Dull or Biscuit 
Porcelain — Soft Phosphated or English Porcelain — Soft Vitreous Porcelain, French and New 
Sdvres— Af^illaceous Soft or Seger's Porcelain — Dull Soft or Parian Porcelain — Dull Felds- 
pathic Soft Porcelain. — Index. 

THE ART OF RIVETING GLASS, CHINA AND 
EARTHENWARE. By J. Howarth. Second Edition. 

1900. Price Is. net ; by post, home or abroad, Is. Id. 

Contents. 

Tools and Materials Required— Wire Used for Rivets — Soldering Solution — Preparation 
for Drilling — Commencement of Drilling— Cementing — Preliminaries to Riveting — Rivets to 
Make— To Fix the Rivets— Through-and-through Rivets— Soldering— Tinning a Soldering-iron 
— Perforated Plates, Handles, etc. — Handles of Ewers, etc.— Vases and Comports — Marble 
and Alabaster Ware — I>ecorating — How to Loosen Fast Decanter Stoppers — China Cements. 



20 

NOTES OP POTTERY CLAYS. Their Distribution, Pro- 
perties, Uses and Analyses of Ball Clays, China Clays and China 
Stone. By Jas. Fairie, F.G.S. 1901. 132 pp. Crown 8vo. Price 
3s. 6d. ; India and Colonies, 4s. ; Other Countries, 4s. 6d. ; strictly net. 

Contents. 

Definitions — Occurrence — Brick Clays — Fire Clays — Analyses of Fire Clays. — Ball Clays — 
Properties — Analyses — Occurrence — Pipe Clay — Black Clay — Brown Clay — Blue Clay — Dor- 
setshire and Devonshire Clays. — China Clay or Kaolin — Occurrence — Chinese Kaolin— Cornish 
Clays — Hensbarrow Granite — Properties, Analyses and Composition of China Clays — 
Method of Obtaining China Clay — Experiments with Chinese Kaolin — Analyses of Chinese 
and Japanese Clays and Bodies — Irish C]ays.~-Chinese Stone— Composition — Occurrence — 
Analyses. — Index. 

PAINTING ON GLASS AND PORCELAIN AND 
ENAMEL PAINTING. A Complete Introduction to the 

Preparation of all the Colours and Fluxes used for Painting on Porce- 
lain, Enamel, Faience and Stoneware, the Coloured Pastes and Col- 
oured Glasses, together with a Minute Description of the Firing of 
Colours and Enamels. On the Basis of Personal Practical Experience 
of the Condition of the Art up to Date. By Felix Hermann, Technical 
Chemist. With Eighteen Illustrations. 300 pp. Translated from the 
German second and enlarged Edition. 1897. Price 10s. 6d. ; India 
and Colonies, lis.; Other Countries, 12s.; strictly net. 

Contents. 

History of Glass Pamting. — Chapters I., The Articles to be Painted : Glass, Porcelainr 
Enamel, Stoneware, Faience. — II., Pigments: 1, Metallic Pigments: Antimony Oxide, Naples 
Yellow, Barium Chromate, Lead Chromate, Silver Chloride, Chromic Oxide. — III., Fluxes: 
Fluxes, Felspar, Quartz, Purifying Quartz, Sedimentation, Quenching, Borax, Borafcic Acid^ 
Potassium and Sodium Carbonates, Rocaille Flux. — IV., Preparation or the Colours for Glass 
Painting. — V., The Colour Pastes. — VI., The Coloured Glasses. — VII., Composition of the 
Porcelam Colours. — VIII., The Enamel Colours: Enamels for Artistic Work.— IX., Metallic 
Ornamentation: Porcelain Gilding, Glass Gilding. — X., Firing the Colours: 1, Remarks on 
Firing: Firing Colours on Glass, FiringColours on Porcelain; 2, The Muffle. — XI., Accidents- 
occasionally Supervening during the Process of Firing. — XII., Remarks on the Different 
Methods or Painting on Glass, Porcelain, etc. — Appendix: Cleaning Old Glass Paintings. 

Press Opinions. 

" Mr. Hermann, by a careful division of his subject, avoids much repetition, yet makes- 
sufficiently clear what is necessary to be known in each art. He gives very many formulae : 
amd his hints on the various applications of metals and metallic lustres to glass and porcelains 
will be found of much interest to the amateur." — Art Amateur, New York. 

" For the unskilled and amateurs the name of the publishers will be sufficient guarantee for 
the utility and excellence of Mr. Hermann's work, even if they are already unacquainted unth 
the author. . . . The whole cannot fail to be both of service and interest to glass workers and 
to potters generally, especially those employed upon high-class work." — Staffordshire Sentinel. 

** In Painting on Glass and Porcelain the author has dealt very exhaustively with the 
technical as distinguished from the artistic side of his subject, the work being entirely devoted 
to the preparation of the colours, their application and firing. For manufacturers and students 
it will be a valuable work, and the recipes which appear on almost every page form a very 
valuable feature. The author has gained much of his experience in the celebrated Sevres^ 
manufactory, a fact which adds a good deal of authority to the work." — Builders Journal. 

" The compiler displays that painstaking research characteristic of his nation, and goes at 
length into the question of the chemical constitution of the pigments and fluxes to be used in 
glass-painting, proceeding afterwards to a description of the methods of producing coloured 
glass of all tints and shades. . . . Very careful instructions are given for the chemical and 
mechanical preparation of the colours used in glass-staining and porcelain-painting; indeed, 
to the china painter such a book as this should be of permanent value, as the author claims to 
have tested and verified every recipe he includes, and the volume also comprises a section de- 
voted to enamels both opaque and translucent, and another treating of the firing of porcelain,, 
and the accidents that occasionally supervene in the furnace." — Datly Chronicle. 

A Reissue of 
THE HISTORY OP THE STAFFORDSHIRE POTTER- 
IES; AND THE RISE AND PROGRESS OF THE 
MANUFACTURE OP POTTERY AND PORCELAIN. 

With References to Genuine Specimens, and Notices of Eminent Pot- 
ters. By Simeon Shaw. (Originally Published in 1829.) 265 pp. 
1900. Demy 8vo. Price 7s. M. ; India and Colonies, 8s. ; Other 
Countries, 8s. 6d. ; strictly net. 



21 
Contents. 

Introductory Chapter showing the position of the Pottery Trade at the present time 
1899).— Chapters I., PreliminarK Remarks.— 11., The Potteries, coofiprising Tunstall, 
Brownhills, Greenfield and New Field, Golden Hill, Latebrook, Green Lane, Burslem, Long- 
port and Dale Hall, Hot Lane and Cobridge, Hanley and Shelton, Btruria, Stoke, Penkhull, 
Fenton, Lane Delph, Foley, Lane End. — III., On the Origin off the Art, and its Practice 
among the early Nations.— IV., Manuffacture off Pottery, prior to 1700.— V., The Introduc- 
tion off Red Porcelain by Messrs. Elers, of Bradwell, 1690.— VI., Progress off the Manu- 
acture from 1700 to Mr. Wedgwood's commencement in 1760.— VII. Introduction off Fluid 
Qiaze. — Extension of the Manufacture of Cream Colour. — Mr. Wedgwood's Queen's Ware. — 
Jasper, and Appointment of Potter to Her M9jesty. — Black Printing. — VIII., Introduction 
off Porcelain. Mr. W. Littler's Porcelain. — Mr. Cookworthy's Discovery of Kaolin and 
Petuntse, and Patent. — Sold to Mr. Champion — resold to the New Hall Com. — Extension of 
Term.— IX., Blue Printed Pottery. Mr. Turner, Mr. Spode (1), Mr. Baddeley, Mr. Spode 
(2), Messrs. Turner, Mr. Wood, Mr. Wilson, Mr. Minton. — Great Change in Patterns of Blue 
Printed. — ^X., Introduction off Lustre Pottery. Improvements in Pottery and Porcelain 
subsequent to 1800. 

Press Opinions. 

" There is much curious and useful information in the work, and the publishers have rendered 
the public a service in reissuing it." — Burton Mail. 

** Copies of the original work are now of considerable value, and the facsimile reprint now 
issued cannot but prove of considerable interest to all interested in the great industry." — Derby 
Mercury. 

** The book will be especially welcomed at a time when interest in the art of pottery manu- 
facture commands a more widespread and general interest than at any previous time." — 
Wolverhampton Chronicle. 

" This work is all the more valuable because it gives one an idea of the condition of affairs 
existing in the north of Staffordshire before the great increase in work and population due to 
modem developments." — Western Morning News. 

. . The History gives a graphic picture of North Staffordshire at the end of the last and 
the beginning of the present century, and states that in 1829 there was * a busy and enterprising 
community ' m the Potteries of fifty thousand persons. . . . We commend it to our readers as 
a most entertaining and instructive publication." — Staffordshire Sentinel. 

A Reissue of 

THE CHEMISTRY OF THE SEVERAL NATURAL 
AND ARTIFICIAL HETEROGENEOUS COM- 
POUNDS USED IN MANUFACTURING POR- 
CELAIN, GLASS AND POTTERY. By Simeon Shaw. 

(Originally published in 1837.) 750 pp. 1900. Royal 8vo. Price 14s. ; 
India and Colonies, 15s. ; Other Countries, 16s. 6d. ; strictly net. 

Contents. 

PART I., ANALYSIS AND MATERIALS.— Chapters I., introduction : Laboratory and 
Apparatus ; Elements : Combinative Potencies, Manipulative Processes for Analysis and 
Reagents, Pulverisation, Blow-pipe Analysis, Humid Analysis, Preparatory Manipulations, 
General Analytic Processes, Compounds Soluble in Water, Compounds Soluble only in Acids, 
Compounds (Mixed) Soluble in Water, Compounds (Mixed) Soluble in Acids, Compounds 
Mixed) Insoluble, Particular Analytic Processes. — II., Temperature: Coal, Steam Heat for 
Printers* Stoves. — III., Acids and Alkalies : Boracic Acid, Muriatic Acid, Nitric Acid, Sul- 
phuric Acid, Potash, Soda, Lithia, Calculation of Chemical Separations. — IV., The Earths : 
Alumine, Clays, Silica, Flint, Lime, Plaster of Paris, Magnesia, Barytes, Felspar, Grauen (or 
China Stone), China Clay, Chert. — V., IVIetals : ReciprocalCombinative Potencies of the Metals, 
Antimony, Arsenic, Chromium, Green Oxide, Cobalt, Chromic Acid, Humid Separation of 
Nickel from Cobalt, Arsenite of Cobalt, Copper, Gold, Iron, Lead, Manganese, Platinum, Silver, 
Tin, Zinc. 

PART II., SYNTHESIS AND COMPOUNDS.— Chapters I., Sketch of the Origin and 
Progress of the Art. — II., Science of Mixing : Scientific Principles of the Manufacture, Com- 
binative Potencies of the Earths. — III., Bodies : Porcelain — Hard, Porcelain — Fritted Bodies, 
Porcelain — Raw Bodies, Porcelain — Soft, Fritted Bodies, Raw Bodies, Stone Bodies, Ironstone, 
Dry Bodies, Chemical Utensils, Fritted Jasper, Fritted Pearl, Fritted Drab, Raw Chemical 
Utensils, Raw Stone, Raw Jasper, Raw Pearl, Raw Mortar, Raw Drab, Raw Brown, Raw Fawn, 
Raw Cane, Raw Red Porous, Raw Egyptian, Earthenware, Queen's Ware, Cream Colour, Blue 
and Fancy Printed, Dipped and Mocha, Chalky, Rings, Stilts, etc. — IV., Qlazes : Porcelain — 
Hard Fritted, Porcelain — Soft Fritted, Porcelain — Soft Raw, Cream Colour Porcelain, Blue 
Printed Porcelain, Fritted Glazes, Analysis of Fritt, Analysts of Glaze, Coloured Glazes, Dips, 
Smears and Washes; Glasses: Flint Glass, Coloured Glasses, Artificial Garnet, Artificial 
Emerald, Artificial Amethyst, Artificial Sapphire, Artificial Opal, Plate Glass, Crown Glass, 
Broad Glass, Bottle Glass, Phosphoric Glass, British Steel Glass, Glass-Staining and Painting, 
Engraving on Glass, Dr. Faraday's Experiments. — ^V., Colours: Colour Makmg, Fluxes or 
SoWents, Components of the Colours; Reds, etc., from Qold, Carmine or Rose Colour, 
Purple, Reds, etc., from Iron, Blues, Yellows, Greens, Blacks, White, Silver for Burnishing, 
Gold for Burnishing, Printer's Oil, Lustres. 



22 

PART III., TABLES OF THE CHARACTERISTICS OF CHEMICAL SUB- 
STANCES. — Preliminary Remarks, Oxygen (Tables), Sulphur and its Compounds, Nitrogen 
ditto. Chlorine ditto. Bromine ditto, Iodine ditto, Fluorine ditto. Phosphorous ditto. Boron ditto. 
Carbon ditto. Hydrogen ditto, Observations, Ammonium and its Compounds (Tables), Thorium 
ditto. Zirconium ditto. Aluminium ditto. Yttrium ditto, Glucinum ditto. Magnesium ditto. 
Calcium ditto, Strontium ditto, Barium ditto. Lithium ditto, Sodium and itsr Compounds 
Potassium ditto. Observations, Selenium and its Compounds (Tables), Arsenic ditto. Chromium 
ditto. Vanadium ditto, Molybdenum ditto, Tungsten ditto, Antimony ditto. Tellurium ditto, 
Tantalum ditto, Titanium ditto, Silicium ditto, Osmium ditto. Gold ditto. Iridium ditto. Rhodium 
ditto, Platinum ditto. Palladium ditto. Mercury ditto. Silver ditto, Copper ditto. Uranium ditto. 
Bismuth and its Compounds, Tin ditto. Lead ditto. Cerium ditto. Cobalt ditto. Nickel ditto, 
Iron ditto. Cadmium ditto, Zinc ditto. Manganese ditto, Observations, Isomorphous Groups, 
Isomeric ditto, Metameric ditto, Polymeric ditto. Index. 

Press Opinions. 

" This interesting volume has been kept from the pencil of the modern editor and reprinted 
in its entirety by the enterprising publishers of The Pottery Gazette and other trade Journals. 
. . . There is an excellent historical sketch of the origin and progress of the art or pottery 
which shows the intimate knowledge of classical as well as (the then) modem scientific litera- 
ture possessed by the late Dr. Shaw ; even the etymology of many of the Staffordshire place- 
names is given."— -G/asg'ow Herald. 

" The historical sketch of the origin and progress of pottery is very interesting and instruc- 
tive. The science of mixing is a problem of great importance, and the query how the natural 
products, alumma and silica can be compounded to form the best wares may be solved by the 
aid of chemistry instead of by guesses, as was formerly the case. This portion of the book may 
be most suggestive to the manufacturer, as also the chapters devoted to the subject of glazes, 
glasses and colours." — Birmingham Post. 

" Messrs. Scott, Greenwood & Co. are doing their best to place before the pottery trades 
some really good books, likely to aid the Staffordshire manufacturers, and their spirited enter- 
prise is worthy of encouragement, for the utility of technical literature bearing upon the 
I ractical side of potting ^oes without saying. . . . They are to be congratulated on . their 
enterprise in republishing it, and we can only nope that they will meet wiui the support they 
deserve. It seems to be a volume that is worth looking through by both manufacturers and 
operatives alike, and all local institutions, at any rate, should secure copies.'* — Staffordshire 
Sentinel. 



Paper Making. 



THE DYEING OP PAPER PULP. A Practical Treatise for 

the use of Papermakers, Paperstainers, Students and others. By 
Julius Erfurt, Manager of a Paper Mill. Translated into English 
and Edited with Additions by Julius Hubner, F.C.S., Lecturer on 
Papermaking at the Manchester Municipal Technical School. With 
Illustrations and 167 patterns Of paper dyed in the pulp. Royal 

8vo, 180 pp. 1901. Price 15s.; India and Colonies, 16s.; Other 
Countries, 20s. ; strictly net. Limited edition. 

Contents. 

I., Behaviour off the Paper Fibres during the Process off Dyeing, Theory off the 
Mordant — Cotton ; Flax and Hemp; Esparto; Jute; Straw Cellulose; Chemical and Mechani- 
cal Wood Pulp; Mixed Fibres; Theory of Dyeing.— II., Colour Fixing Mediums (Mordants) 

— Alum; Aluminium Sulphate; Alummium Acetate; Tin Crystals (Stannous Chloride); Cop- 
peras (Ferrous Sulphate); Nitrate of Iron (Ferric Sulphate) ; Pyrolignite of Iron (Acetate of 
Iron) ; Action of Tannic Acid ; Importance of Materials containing Tannin ; Treatment with 
Tannic Acid of Paper Pulp intended for dyeing; Blue Stone (Copper Sulphate) ; Potassium 
Bichromate; Sodium Bichromate; Chalk (Calcium Carbonate); Soda Crystals (Sodium Car- 
bonate); Antimony Potassium Tartrate (Tartar Emetic). — III., inffluence of the Quality of 
the Water Used. — IV., Inorgfanic Colours — 1. Artificial Mineral Colours: Iron Buff; Man- 
ganese Bronze; Chrome Yellow (Chromate of Lead); Chrome Orange (Basic Chromate of 
Lead) ; Red Lead ; Chrome Green ; Blue with Yellow Prussiate ; Prussian Blue ; Method for 
Producing Prussian Blue free from Acid; Ultramarine — 2. Natural Mineral Colours (Eartii 
Colours) : Yellow Earth Colours ; Red Earth Colours ; Brown Earth Colours ; Green, Grey and 
Black Earth Colours; White Earth Colours; White Clay (China Clay); White Gypsum; 
Baryta; Magnesium Carbonate; Talc, Soapstone. — V., Orgpanic Colours — 1. Colours of 
Vegetable and Animal Origin : {a) Substantive (Direct Dyeing) Colouring Matters : Annatto ; 
Turmeric ; Safflower ; (6) A djective (Indirect Dyeing) Colouring Matters : Redwood ; Cochineal ; 
Weld ; Persian Berries ; Fustic Extract ; Quercitron ; Catechu (Cutch) ; Logwood Extract — 2, 
Artificial Organic (Coal Tar) Colours: Acid Colours; Basic Colours; Substantive (Direct 
Dyeing) Colours; Dissolving of the Coal Tar Colours; Auramine°°; Naphthol Yellow S^; 

euinoline Yellow®; Metanil Yellow<>; Paper Yellow^; Azoflavine RS^ S°; Cotton Yellow 
XX and Rxx; Orange IF; Chrysoidine Ao°, RL°°; Vesuvine ExtraO®; Vesuvine BC°°; Fast 



23 

Brown^Naphthylsunine Brown^ : Water Blue IN° ; Water Blue TB^ ; Victoria Blue B^ ; Methy- 
lene Blue MD<»; Nile Blue R<»: New Blue S°°; Indoine Blue BB<»: Bo8ine442 Nx; Phloxine 
BBN ; Rhodamine B°°; Rhodamine 6G^; Naphthylamine Red 0° ; Past Red A*'; Cotton 
Scarlet° ; Erythrine RR° ; Erytbrine X° ; Erythrtne P° ; Ponceau 2 Ro ; Fast Ponceau G° and 
B°; Paper Scarlet P°°; Saffranine PP~; Magenta Powder A°°; Acetate of Magenta°° ; 
Cerise D 10°° ; Methyl Violet BB<='° ; Crystal VioIet5>° ; Acid Violet 3 BN°, 4 R° ; Diamond 
Green B°°; Nigrosine WL°; Coal Black<^; Brilliant Black B°.— VI., Practical Application 
of the Coal Tar Coiours according to their Properties and their Behavionr towards 
the Different Paper Fibres — Coal "Hir Colours, which rank foremost, as far as their fastness 
to light is concerned ; Colour Combinations with which colourless or nearly colourless Back- 
water is obtained ; Colours which do not bleed into White Fibres, for Blotting and Copying 
Paper Pulp; Colours which produce the best results on Mechanical Wood and on Unbleached 
Sulphite Wood; Dyeing of Cotton, Jute and Wool Half-stuff for Mottling White or Light 
Coloured Papers; Colours suitable for Cotton; Colours spectallv suitable for Jute Dyeing; 
Colours suitable for Wool Fibres.— VII., Dyed Patterns on Various Pulp Mixtures- 
Placard and Wrapping Papers; Black Wrapping and Cartridge Papers; Blotting Papers; 
Mottled and Marbled Papers made with Coloured Linen, Cotton and Union Rags, or with 
Cotton, Jute, Wool and Sulphite Wood Fibres, dyed specially for this purpose; Mottling with 
Dark Blue Linen ; Mottling with Dark Blue Linen and Dark Blue Cotton ; Mottling with Dark 
Blue Cotton ; Mottling with Dark Blue and Red Cotton ; Mottling with Dark Red Cotton ; 
Mottling of Bleached Stuff, with 3 to 4 per cent, of Dyed Cotton Fibres ; Mottling with Dark 
Blue Union (Linen and Wool or Cotton Warp with Wool Weft) ; Mottling with Blue Striped 
Red Union ; Mottling of Bleached Stuff with 3 to 4 per cent, of Dyed Wool Fibres ; Mottling 
of Bleached Stuff with 3 to 4 per cent, of Dyed Jute Fibres ; Mottling of Bleached Stuff with 
S to 4 per cent, of Dyed Sulphite Wood Fibres; Wall Papers; Packing Papers.— VIII., 
Dyeing: to Shade— Indfex. 

Press Opinions. 

" The book is one that is of value to every one connected with the colouring of paper." — 
Paper Trade Journal. 

"The great feature of the volume is undoubtedly the series of actual patterns of dyed 
papers, 157 in all — twelve of which, made in England, have been added to the original German 
series. Detailed formulae are given for the preparation of the pulp for each, and the tints of 
the samples practically form a key, by means of which the accuracy of the student's or 
practitioner's experiments can be tested. . . . On the whole the publication is one of distinct 
importance to the trade, and will no doubt speedily become a standard work of reference 
amongst papermakers, both in the ' lab.' and the office, as well as being an excellent text-book 
for the use of students in the increasing number of technical institutes in which papermaking 
is taught." — World's Paper Trade Review. 

Enamelling on Metal. 

ENAMELS AND ENAMELLING. An Introduction to the 
Preparation and Application of all Kinds of Enamels for Technical and 
Artistic Purposes. For Enamel Makers, Workers in Gold and Silver, 
and Manufacturers of Objects of Art. By Paul Randau. Translated 
from the German. With Sixteen Illustrations. 180 pp. 1900. Price 
10s. 6d. ; India and Colonies, lis. ; Other Countries, 12s. ; strictly net. 

Contents. 

I., Introduction. — XL, Composition and Properties of Glass. — III., Raw Materials for the 
Manufacture of Enamels. — IV., Substances Added to Produce Opacity. — V., Fluxes. — VI., Pig- 
ments. — VII., Decolorising Agents. — VIII., Testing the Raw Materials with the Blow-pipe 
Flame. — IX., Subsidiary Materials. — X., Preparing the Materials for Enamel Making. — XL, 
Mixing the Materials. — ^XII., The Preparation of Technical Enamels, The Enamel Mass. — 
XIII., Appliances for Smelting the Enamel Mass. — XIV., Smelting the Charge. — XV., Com- 
position of Enamel Masses. — XVI., Composition of Masses for Ground Enamels. — XVII., 
Composition of Cover Enamels. — XVIII., Preparing the Articles for Enamelling. — XIX., 
.Applying the Enamel. — XX., Firing the Ground Enamel. — XXI., Applying and Firing the 
Cover Enamel or Glaze. — XXII., Repairing Defects in Enamelled Ware. — XXIII., Enamelling 
Articles of Sheet Metal.-^XXIV., Decorating Enamelled Ware.— XXV., Specialities in Ena- 
melling. — XXVI., Dial-plate Enamelling. — XXVII., Enamels for Artistic Purposes, Recipes 
for Enamels of Various Colours. — Index. 

Press Opinions. 

" Should prove of great service to all who are either engaged in or interested in the art of 
ensimelling."— Jewellers and Watchmakers' Trade A dvertiser. 

" I must inform you that this is the best book ever I have come across on enamels, and it is 
worth double its cost." — J. Minchin, Jr., Porto, Portugal, 22nd July, 1900. 

" This is a very useful and thoroughly practical treatise, and deals with every branch of the 
enameller's art. The manufacture of enamels of various colours and the methods of their 
application are described in detail. Besides the commoner enamelling processes, some of the 
more important special branches of the business, such as cloisonne work are dealt with. The 
work is well got up, and the illustrations of apparatus are well executed. The translator is 
evidently a man well acquainted both with the German language and the subject-matter of the 
book." — Invention. 



24 

" This is a most welcome volume, and one for which we have long waited in this country. 
For years we have been teaching design applied to enamelling as well as to several other 
crafts, but we have not risen to the scientific side of the question. Here is a handbook dealing 
with the composition and making of enamels for application to metals for the most part, but 
also for other allied purposes. It is written in a thoroughly practical way, and its author — 
Paul Randau — has made its subject a very particular study. The result, like almost all things 
which come from the German chemical expert, is a model of good workmanship and arrange- 
ment, and no one who is in search of a handbook to enamelling, no matter whether he is a 
craftsman producing his beautiful translucent colours on gold, silver and copper, or the hollow- 
ware manufacturer making enamelled saucepans and kettles, can wish tor a more useful 
practical manual." — Birmingham Gazette. 

THE ART OF ENAMELLING ON METAL. By W. 

Norman Brown. Twenty-eight Illustrations. Crown 8vo. 60 pp. 
1900. Price 2s. 6d. ; Abroad, 3s. ; strictly net. 

Contents. 

Chapters I., History — Cloisonn6 — Champs Lev6 — ^Translucent Enamel — Surface Painted 
Enamels. — II., Cloisonn6^<^hamps Lev6s — Translucent — Painted. — III., Painted Enamel — 
Apparatus — Furnaces and Muffles for Firing. — IV., The Copper Base or Plate — Planishing — 
Cloisons — Champ Lev6 Plates. — V., Enamels — Trituration — Washing — Coating a Plate with 
Enamel — Firing Ordinary Plaques for Painting — Designing — Squaring off. — VI., Designs for 
Cloisonn6 — Designs for Painted Enamels — Technical Processes — Brushes, etc., — Colours — 
Grisaille — Full-coloured Designs. 

Press Opinion. 

"The information conveyed in The Art of Enamelling on Metal is as complete as can be ex- 
pected in a manual of ordinary length, and is quite ample in all respects to start students in a 
most interesting branch of decorative art. All necessary requisites are fully described and 
illustrated, and the work is one, indeed, which any one may pursue with interest, for those who 
are interested artistically in enamels are a numerous body." — Hardware Metals and Machinery. 



Books on Textile and Dyeing 

Subjects. 

THE TECHNICAL TESTING OF YARNS AND TEX- 
TILE FABRICS. With Reference to Official Specifica- 

tions. Translated from the German of Dr. J. Herzfeld. Second 
Edition. Sixty-nine Illustrations. 200 pp. Demy 8vo. 1901. Price 
10s. 6d. ; India and Colonies, lis.; Other Countries, 12s. ; strictly net. 

Contents. 

Yam Testing. III., Determinins: thn Yarn Number.— IV., Testing the Length of 
Yams. — v.. Examination of the External Appearance of Yarn. — VI., Determininc' the 
Twist of Yam and Twist.— VII., Determination of Tensile Strength and Elasttcity.— 
VIII., Estimating the Percentage of Pat in Yam.— IX., Determination of Moisture 

(Conditioning).— Appendix. 

Press Opinions. 

" It would be well if our English manufacturers would avail themselves of this important 
addition to the extensive list of German publications which, by the spread of technical infor> 
mation, contribute in no small degree to the success, and sometimes to the supremacy, of 
Germany in almost every branch of textile manufacture." — Manchester Courier. 

'* This is probably the most exhaustive book published in English on the subject dealt with. 
. . . We have great confidence in recommending the purchase of this book by all manu- 
facturers of textile goods of whatever kind, and are convinced that the concise and direct way 
in which it is written, which has been admirably conserved by the translator, renders it 
peculiarly adapted for the use of English readers." — Textile Recorder. 

" A careful study of this book enables one to say with certainty that it is a standard work on 
the subject. Its importance is enhanced greatly by the probability that we have here, for the 
first time in our own language, in one volume, a full, accurate, and detailed account, by a prac- 
tical expert, of the best technical methods for the testing of textile materials, whether in the 
raw state or in the more or less finished product." — Glasgow Herald. 

" The author has endeavoured to collect and arrange m systematic form for the first time 
all the data relating to both physical and chemical tests as used throughout the whole of the 
textile industry, so that not only the commercial and textile chemist, who has frequently to 
reply to questions on these matters, but also the practical manufacturer of textiles and his 
subordinates, whether in spinning, weaving, dyeing, and finishing, are catered for. . . . The 
book is profusely illustrated, and the subjects of these illustrations are clearly described." — 
Textile Manufacturer. 



25 
DECORATIVE AND FANCY TEXTILE FABRICS. 

With Designs and Illustrations. By R. T. Lord. A Valuable Book for 
Manufacturers and Designers of Carpets, Damask, Dress and all Textile 
Fabrics. 200 pp. 1898. Demy8vo. 132 Designs and Illustrations. Price 
7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 

Contents. 

Chapters I., A Few Hints on Designing Ornamental Textile Fabrics. — II., A Few Hints on 
Designing Ornamental Textile Fabrics (continued). — III., A Few Hints on Designing Orna- 
mental Textile Fabrics (continued). — IV., A Few Hints on Designing Ornamental Textile 
Fabrics (continued). — V., Hints for Ruled-paper Draughtsmen. — VI., The Jacquard Machine. — 
VII., Brussels and Wilton Carpets. — VIII., Tapestry Carpets. — IX., Ingrain Carpets. — X., 
Axminster Carpets. — XL, Damask and Tapestry Fabrics. — XII., Scarf Suks and Ribbons. — 
XIII., Silk Handkerchiefs.— XIV., Dress Fabrics.— XV., Mantle Cloths.— XVI., Figured Plush. 
—XVII., Bed Quilts.— XVIII., Calico Printing. 

Press Opinions. 

** The book can be strongly recommended to students and practical men." — Textile Coloutist* 

" Those engaged in the designing of dress, mantle tapestry, carpet and other ornamental 
textiles will find this volume a useful work of reference." — Leeds Mercury. 

" The bo*k is to be commended as a model manual, appearing at an opportune time, since 
every dav is making known a growing desire for development in British industrial art." — 
Dundee Advertiser. 

" Designers especially, who desire to make progress in their calling, will do well to take the 
hints thrown out in the first four chapters on * Designing Ornamental Textile Fabrics '." — 
Nottingham Daily Guardian. 



POWER-LOOM WEAVING AND YARN NUMBERING, 

According to Various Systems, with Conversion Tables. An Auxiliary 
and Text-book for Pupils of Weaving Schools, as well as for Self- 
Instruction and for General Use by those engaged in the Weaving 
Industry. Translated from the German of Anthon Gruner. With 

Twenty-8ix Diagrams in Colours. 150 pp. 1900. Crown 8vo. Price 

7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 

Contents. 

I., Power-Loom Weaving: in Qeneral. Various Systems of Looms.— II., Mountinsr 
and Startinfir tlie Power- Loom. English Looms. — Tappet or Treadle Looms. — Dobbies. — 
IIL, OeneralRemarlcson the Numbering, Reeling and Pacldnsrof Yam.— Appendix.— 
Useful Hints. Calculating Warps. — Weft Calculations.— Calculations of Cost Price in Hanks. 

Press Opinions. 

" A long-felt want in the weaving industry has been supplied^by the issue of a cheap volume 
dealing with the subject." — Belfast Evening Telegraph. 

"The work has been clearly translated from the German and published with suitable 
illustrations. . . . The author has dealt very practically with the subject." — Bradford Daily 
Telegraph. 

** The book, which contains a number of useful coloured diagrams, should prove invaluable 
to the student, and its handy form will enable it to become a companion more than some cum- 
brous work." — Cotton Factory Times. 

" The book has been prepared with great care, and is most usefully illustrated. It is a capital 
text-book for use in the weaving schools or for self-instruction, while all engaged in the weaving 
industry will find its suggestions helpful." — Northern Daily Telegraph. 

"The various systems are treated in a careful manner ; also the different looms and their 
manufacture, as well as the whole processes of the work. Yarn numbering according to various 
systems, with conversion tables and numerous coloured diagrams, materially assist to a clear 
comprehension of the subject." — Northern Whi^. 

"The ' inside ' managers of our textile mills in which the work is complex or greatly varied^ 
and where yarns of different materials are in use, will find this work convenient for reference in 
case of novelty or difficulty. We may also say the same in relation to the textile student. Ita 
description of the parts of the loom and their functions will be of use to the latter, being of the 
most elementary kind." — Textile Mercury. 

" The author attempts to fill a ^ap in weaving literature caused by the neglect of many 
obscure points connected with the mdustry. A short review is given of the power-loom as a 
whole, followed by a description of the different parts of the machinery with their advantages 
and defects. . . . The book is severely technical, but must on that account be very valuable to 
the pupil who is determined to master this industrial art." — Cheshire County News. 

" It is clear and concise, and gives just that knowledge in quality and amount which any 

student of the weaving industry ought to consider as a minimum necessary for his thorough 

comprehension of his future profession. The handiness and variety of the information com- 

orised in Section III., dealing with the numbering and reeling of yarns employed in the various 

.Stems in different countries* struck us as particularly useful " — North British Daily Mail. 



26 

"This work brings before weavers who are actually engaged in the various branches of 
fabrics, as well as the technical student, the different parts of the general run of power-looms in 
«uch a manner that the parts of the loom and their bearing to each other can be readily under- 
stood. . . . The work should prove of much value, as it is in every sense practical, and is put 
before the reader in such a clear manner that it can be easily understood." — Textile Industries. 

"The book under notice is intended as an instructor to those engaged in power-loom weaving, 
and, judging by its compilation, the author is a thorough master of the craft. It is not over- 
loaded with details, and he manages to compress in a book of some 150 pages all that one can 
possibly wish to know about the different parts of the machinery, whether of English or foreign 
make, and for whatever kind of cloth required. A comprehensive summary is suso included of 
the various yarns and methods of numbering them, as well as a few useful hints and a number 
■of coloured diagrams for mandarin weavings. The book is printed in bold, legible type, on 
good paper, has a copious index, and is well and strongly bound." — Ashton-under-Lyne Herald. 

" In dealing with the complicated parts of various classes of power-looms, the writer, who is 
one of the professors at the Royal Weaving School of Asch, brings to the work a thorough 
knowledge of the subject, and, what is of great value, he has the gift of communicating his 
knowledge in a way which is easily understood. The smallest details of loom-setting are 
entered into, and a full explanation of problems, which are a source of anxiety to many en- 
gaged in overlooking, is given. Students will find the work an admirable text-book, and all 
who are interested in weaving will see in it a valuable addition to the literature on this subject. 
. . The book is in small compass, and is crowded with valuable information." — Bradford 
Observer. 

COLOUR: A HANDBOOK OF THE THEORY OP 
COLOUR. By George H. Hurst, F.C.S. With Ten 

Coloured PlatOS and Seventy-two Illustrations. 160 pp. Demy 8vo. 
1900. Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; 
strictly net. 

Contents. 

Chapters I., Colour and Its Production. Light, Colour, Dispersion of White Light 
Methods of Producing the Spectrum, Glass Prism and Diffraction Grating Spectroscopes, The 
Spectrum, Wave Motion of Light, Recomposition of White Light, Hue, Luminosity, Purity 
•of Colours, The Polariscope, Phosphorescence, Fluorescence, Interference. — IL, Cause of 
Colour in Coloured Bodies. Transmitted Colours, Absorption Spectra of Colouring 
Matters. — III., Colour Phenomena and Theories. Mixing Colours, White Light from 
Coloured Lights, Efl^ct of Coloured Light on Colours, Complementary Colours, Young- 
Helmholtz Theory, Brewster Theory, Supplementary Colours, Maxwell's Theory, Colour 
Photography.— IV., The Physiology of Li^ht. Structure of the Eye, Persistence of Vision, 
Subjective Colour Phenomena, Colour Blindness. — ^V., Contrast. Contrast, Simultaneous 
-Contrast, Successive Contrast, Contrast of Tone. Contrast of Colours, Modification of Colours 
by Contrast, Colour Contrast in Decorative Design.— VI., Colour in Decoration and 
Design. Colour Harmonies, Colour Equivalents, Illumination and Colour, Colour and 
TextUe Fabrics, Surface Structure and Colour. — VIL, Measurement of Colour. Colour 
Patch Method, The Tintometer, Chromometer. 

Press Opinions. 

" This useful little book possesses considerable merit, and will be of great utility to those for 
-whom it is primarily intended." — Birmingham Post. 

" It will be found to be of direct service to the majority of dyers, calico printers and colour 
-mixers, to whom we confidently recommend it." — Chemical Trade Journal. 

" It is thoroughly practical, and gives in simple language the why and wherefore of the many 
•colour phenomena which perplex the dyer and the colourist." — Dyer and Calico Printer. 

" We have found the book very interesting, and can recommend it to all who wish to master 
the different aspects of colour theory, with a view to a practical application of the knowledge so 
gained." — Chemist and Druggist. 

" Mr. Hurst's Handbook on the Theory of Colour will be found extremely useful, not only to 
the art student, but also to the craftsman, whose business it is to manipulate pigments and 
dyes." — Nottingham Daily Guardian. 

TEXTILE RAW MATERIALS AND THEIR CON- 
VERSION INTO YARNS. (The Study of the Raw 
Materials and the Technology of the Spinning Process.) Text- book for 
Textile, Trade and Higher Technical Schools. By Julius Zipser. 
Translated from German by Charles Salter. 302 Illustrations. 
480 pp. Demy 8vo. 1901. Price 10s. 6d. ; India and Colonies, lis.; 
Other Countries, 12s. ; strictly net. 

Contents. 

Raw Materials : Cotton — Wool — Flax — Hemp — Jute — Hair — Shearing Sheep— Goat 
"Wool — Silk — Detection and Estimation of Textile Raw Materials in Yarns and Fabrics — Tests. 
—The Technology of Spinninsf. Cotton Spinning : Bale Breakers— Carding— Combing 
— Roving — Mule Frames — Yarn Testing — Humidifiers. Flax Spinning* : Tow Spinning — 
String Spinning— Carded Woollen Yarn— Belt Condenser — Fine Spinning — ^Yarn Numbering. — 
Manufacture of True Worsted Yam: Semi-Worsted Yarns.— Artificial Wool or 
Shoddy Spinning: Spinning Shoddy.— Index. 



27 
THE COLOUR PRINTING OF CARPET YARNS. A 

Useful Manual for Colour Chemists and Textile Printers. By David 
Paterson, F.C.S. Seventeen Illustrations. 132 pp. DemySvo. 1900. 
Price 7s. 6d. ; India and Colonies, 8s. Other Countries, 8s. 6d. ; strictly 
net. Contents. 

Chapters I., Structure and Constitution of Wool Fibre. — II., Yarn Scouring. — III., Scouring 
Materials. — IV., Water for Scouring. — V., Bleaching Carpet Yams. — VI., Colour Making for 
Yam Printing. — VII., Colour Printing Pastes. — VIII., Colour Recipes for Yarn Printing. — 
IX., Science of Colour Mixing. — X., Matching of Colours. — XL, "Hank" Printing. — XII.» 
Printing Tapestry Carpet Yams. — XIII., Yarn Printing. — XIV., Steaming Printed Yarns. — 
XV., Washing of Steamed Yarns. — XVI., Aniline Colours Suitable for Yam Printing. — XVII.» 
Glossary of Dyes and Dye-wares used in Wood Yarn Printing. — Appendix. 

Press Opinions. 

"The book is worthy the attention of the trade." — Worcester Herald. 

" The treatise is arranged with great care, and follows the processes described in a manner 
at once clear and convincing." — Glasgow Record. 

" A most useful manual dealing in an intelligible and interesting manner with the colour 
printing of carpet yams." — Kidderminster Times. 

" An eminent expert himself, the author has evidently strained every effort in order to make 
his work the standard guide of its class." — Leicester Post. 

" The book, which is admirably printed and illustrated, should fulfil the need of a practical 
guide in the colour printing of carpet yarns. — Nottingham Express. 

"The subject is very exhaustively treated in all its branches. . . . The work, which is very 
well illustrated with designs, machines, and wool fibres, will be a useful addition to our textile 
literature." — Northern Whig. 

" It gives an account of its subject which is both valuable and instructive in itself, and likely 
to be all the more welcome because books dealing with textile fabrics usually have little or 
nothing to sav about this way of decorating them." — Scotsman. 

"The work shows a thorough grasp of the leading characteristics. as well as the minutae of 
the industry, and gives a lucid description of its chief departments. ... As a text-book in 
technical schools where this branch of industrial education is tau^ht,jthe book is valuable, or 
it may be perused with pleasure as well as profit by any one having an interest in textile in- 
dustries." — Dundee Courier. 

"The book bears every mark of an extensive practical knowledge of the subject in all it& 
bearings, and supplies a real want in technical literature. Chapters IX. and X., on the science 
of colour mixing and colour matching respectively, are especially good, and we do not remem* 
ber to have seen the bearing of various kinds of light, and of the changes from one kind of light 
to another on the work of the colourist, so well treated elsewhere." — Dyer and Calico Printer^ 

" It is thoroughly practical, and contains much information which has not hitherto appeared 
in book form. It is pleasing to note that the practical part is not crowded out with purely 
' practical recipes '. A few typical examples are given, and the rest is left to the common sense 
and judgment of the printer or works' chemist. Another pleasing feature is the accounts given 
here and there of the author's own researches on the subject. The work will be of interest to- 
printers of wool generally, and to those engaged in the dyeing of this fibre."— /<'*'^^^^ of '^ 
Society of Dyers and Colourists. 

A PRACTICAL TREATISE ON THE BLEACHING OF 
LINEN AND COTTON YARN AND FABRICS. By 

L. Tailper, Chemical and Mechanical Engineer. Translated from the 
French by John Geddes McIntosh, Lecturer on Chemical Technology, 
London. Demy 8vo. 1901. Price 12s. 6d. ; India and Colonies, 13s. 6d ;. 
Other Countries, 15s. ; strictly net. 

Contents. 

Chapter I. General Considerations on Bleaching. Chapter II. Steeping. Chapter III 
Washing : Its End and Importance — Roller Washing Machines — Wash WheeiCDash Wheel) — 
Stocks or Wash Mill — Squeezing. Chapter IV. Lye Boiling — Lye Boiling with Milk of Lime 
— Lye Boiling with Soda Lyes — Description of Lye Boiling Keirs — Operations of Lye Boiling 
— Concentration of Lyes. Chapter V. Mather and Piatt's Keir — Description of the Keir — 
Saturation of the Fabrics — Alkali used in Lye Boiling — Examples of Processes. Chapter VI. 
Soap— Action of Soap in Bleaching — Quality and Quantity of Soaps to use in the Lye — Soap 
Lyes or Scalds — Soap Scouring Stocks. Chapter VII. Bleaching on Grass or on the Bleach- 
ing Green or Lawn. Chapter VIII. Chemicking — Remarks on Chlorides and their De- 
colourising Action — Chemicking Cisterns — Chemicking — Strengths, etc. Chapter IX. Sours 
— Properties of the Acids — Effects Produced by Acids — Souring Cisterns. Chapter X. 
Drying — Drying by Steam — Drying by Hot Air — Drying by Air. Chapter XI. Damages to 
Fabrics in Bleachmg — Yarn Mildew — Fermentation — Iron Rust Spots — Spots from Contact 
with Wood — Spots incurred on the Bleaching Green — Damages arising from the Machines. 
Chapter XII. Examples of Methods used in Bleaching — Linen — Cotton. Chapter XIII. The 
Valuation of Caustic and Carbonated Alkali (Soda) and General Information Regarding these 
Bodies— Object of Alkalimetry — ^Titration of Carbonate of Soda — Comparative Table of 
Different Degrees of Alkalimetrical Strength — Five Problems relative to Carbonate of Soda 
— Caustic Soda, its Properties and Uses — Mixtures of Carbonated and Caustic Alkali — Note 
oo a Process of Manufacturing Caustic Soda and Mixtures of Caustic and Carbonated Alkali 
(Boda). Chapter XIV. Chlorometry — Titration — Wagner's Chlorometric Method — Prepare- 



28 

tion of Standard Solutions — ^Apparatus for Chlorine Valuation — Alkali in Excess in De- 
colourising Chlorides. Chapter XV. Chlorine and Decolourising Chlorides — Synopsis — 
Chlorine — Chloride of Lime — Hypochlorite of Soda — Brochoki's Chlorozone — Various De- 
colourising Hypochlorites — Comparison of Chloride of Lime and Hypochlorite of Soda. 
Chapter XVI. Water— Qualities of Water — Hardness — Dervaux's Purifier — ^Testing the 
Purified Water— Different Plant for Purification— Filters. Chapter XVH. Bleaching of 
Yarn — Weight of Yam — Lye Boiling— Chemicking — Washing — Bleaching of Cotton Yam. 
Chapter XVIII. The Installation of a Bleach Works— Water Supply— Steam Boilers— Steam 
Distribution Pipes — Engines — Keirs — Washing Machines — Stocks — Wash Wheels — Chemick- 
ing and Souring Cisterns — Various — Buildings. Chapter XIX. Addenda — Energy of De- 
cc^ourising Chlorides and Bleaching by Electricity and Ozone — Energy of Decolourising 
Chlorides — Chlorides — Production of Chlorine and Hypochlorites by Electrolysis — Lunge's 
Process for increasing the intensity of the Bleaching Power of Chloride of Lime — Trilfer's 
Process for Removing the Excess of Lime or Soda from Decolourising Chlorides — Bleaching 
by Ozone. 

THE SCIENCE OF COLOUR MIXING. A Manual in- 

tended for the use of Dyers, Calico Printers and Colour Chemists. By 
David Paterson, F.C.S. Forty -one Illustrations, Five Coloured Platoe, 

and Four Plates showing: Eleven Dyed Speoimens of Fabrics. 132 

pp. Demy 8vo. 1900. Price 7s. 6d. ; India and Colonies, 8s. ; Other 
Countries, 8s. 6d. ; strictly net. 

Contents. 

Chapters I., Colour a Sensation; Colours of Illuminated Bodies; Colours of Opaque and 
Transparent Bodies; Surface Colour. — II., Analysis of Light; Spectrum; Homogeneous 
Colours; Ready Method of Obtaining a Spectrum. — III., Examination of Solar Spectrum; 
The Spectroscope and Its Construction; Colourists' Use of the Spectroscope. — IV.. Colour by 
Absorption ; Solutions and Dyed Fabrics ; Dichroic Coloured Fabrics in Gaslight. — V., Colour 
Primaries of the Scientist versus the Dyer and Artist ; Colour Mixing by Rotation and Lye 
Dyeing; Hue, Purity, Brightness; Tints; Shades, Scales, Tones, Sad and Sombre Colours.— 
VI., Colour Mixing ; Pure and Impure Greens, Orange and Violets; Large Variety of Shades 
from few Colours ; Consideration of the Practical Primaries : Red, Yeuow and Blue. — VIL, 
Secondary Colours ; Nomenclature of Violet and Purple Group ; Tints and Shades of Violet ; 
Changes m Artificial Light. — ^VI 1 1., Tertiary Shades; Broken Hues; Absorption Spectra of 
Tertiary Shades. — Appendix: Four Plates with Dyed Specimens Illustrating Text. — Index. 

Press Opinions. 

" The work has evidently been prepared with great care, and, as far as we can judge, should 
be very useful to the dyer and colourist." — Halifax Courier. 

" The volume, which is clearly and popularly written, should prove of the utmost service to 
all who are concerned with the practical use of colours, whether as dyers or painters." — 
Scotsman. 

"To the practical colourist, and also to technical students, Mr. Paterson 's new work will be 
very welcome We are often asked to recommend books on different subjects, and have no 
hesitation in advising the purchase of the present volume by dyers and calico printers, as con- 
taining a mass of most useful information at a nominal price." — Irish Textile Journal. 

" Mr. Paterson's work not only clearly deals with the theory of colour, but supplies lucid 
^directions for the practical application of the theory. His work will be found exceedingly 
helpful, not only to the practical colourist, but also to students in our textile colleges, by 
forming a useful complement to their class lectures. There are several exquisitely coloured 
plates and a large number of other illustrations of theory and practice in colour blending, and 
also a series of plates with specimens of dyed fabrics attached, in explication of the author's 
views." — Wakefield Express. 

" Mr. Paterson has little to say upon the experimental aspect or on its aesthetics, but much 
upon the theory of colour, especially as it bears upon the question — ^an all-important one to 
dyers, calico pnnters and artists, who have to produce such a variety of shades and tints — of 
the admixture of one colour, upon another. . . . The author is a dyer, and in his concluding 
chapters keeps well before him the special wants and requirements of dyers. He writes 
pleasantly and lucidly, and there is no difficulty in following him, although here and there a 
lapse into ambiguousness occurs. The book is well printed, generously supplied with coloured 
plates, very nicely if not brightly got up ; and the dyed patterns at the end enhance the value 
of the book to the dyer." — Textile Mercury. 

" For some time the proprietors of The Oil and Colourman's Journal have been engaged in 
the publication of a series of practical handbooks intended for the use of those interested in 
certain branches of technology, and the present volume is the latest addition to their list. 
The feature which the works have in common — and it is an all-important one in treatises of 
this sort — is their eminently practical character. The primary aim of the publishers is to 
provide scientific text-books which will be helpful to those who are either actively engaged in 
the practice of the arts in question, or who are studying with that immediate end in view. . . . 
Mr. Paterson speaks with that assured knowledge of an expert, and in the present volume, as 
in that which he has already contributed to the same series, he sets forth the true foundation 
of the art of colouring in a manner at once comprehensive and judicious. . . . For dyers, 
•calico printers and colourists in general, whose desire it is to work with accuracy in their 
respective branches, the treatise will prove an invaluable guide-book, provided the principles 
and methods it describes are studied with intelligence and care. To this end, every encourage- 
ment has been given that well-chosen examples, carefully executed plates and diagrams, and 
an exhaustive index can supply."— G/asg^ow Herald. 



29 

COLOUR MATCHING ON TEXTILES. A Manual in- 
tended for the use of Students of Colour Chemistry, Dyeing and 
Textile Printing. By David Patbrson, F.C.S. Coloured Frontis- 
piece. Twenty-nine Illustrations and Fourteen Specimens of Dyed 
Fabrics Illustrating Text. Demy 8vo. 132 pp. 1901. Price 7s. 6d. ; 
India and Colonies, 8s. ; Other Countries, 8s. ^. ; strictly net. 

Contents. 

Chapters I., Colour Vision and Structure of the Eye — Perception of Colour — Primary 
and Complementary Colour Sensations. — II., Daylight for Colour Matching — Selection of a 
Good Pure Light— Diffused Daylight, Direct Sunlight, Blue Skylight. Variability of Daylight, 
etc., etc. — III., Matching of Hues — Purity and Luminosity of Colours — Matching Bright Hues 
— Aid of Tinted Films — Matching Difficulties Arising from Contrast. — IV., Examination of 
Colours by Reflected and Transmitted Lights — Effect of Lustre and Transparency of Fibres 
in Colour Matching. — V., Matching of Colours on Velvet Pile — Optical Properties of Dye- 
stuffs, Dichroism, Fluorescence. — ^VI., Use of Tinted Mediums — Orange Film — Defects of the 
Eye — Yellowing of the Lens — Colour Blindness, etc. — VII., Matching of Dyed Silk Trimmings 
and Linings and Bindings — Its Difficulties — Behaviour of Shades in Artificial Light — Colour 
Matching of Old Fabrics, etc. — VIII., Examination of Dyed Colours under the Artificial Lights 
— Electric Arc, Magnesium and Dufton, Gardner Lights, Welsbach, Acetylene, etc. — ^Testing 
Qualities of an Illuminant. — IX., Influence of the Absorption Spectrum in Changes of Hue 
under the Artificial Lights — Study of the Causes of Abnormal Modifications of Hue, etc. 

Reissue of 
THE ART OF DYEING WOOL, SILK AND COTTON. 

Translated from the French of M. Hellot, M. Macquer and M. le 

PiLEUR D'Apligny. First Published in English in 1789. Six Plates. 

Demy 8vo. 446 pp. 1901. Price 5s. ; India and Colonies, 5s. 6d. ; 

Other Countries, 6s. ; strictly net. 

Contents. 
Part I., The Art of Dyeing Wool and Woollen Cloth, Stuffs, Yam, Worsted, etc. : 
Introduction. — Chapters I., Of the Vessels and Utensils used in Dyeing. — II., Of the Fixed 
lod Fugitive, commonly called Great and Little Dye. — III., Of Colours in Grain. Dyeing 
Wool : IV., Of Blue.— v.. Of the Pastel Vat— Directions for the Proper Management of the 
* Vat — Indications when the Vat has Suffered by too much or too little Lime, the two extremes 

which ought carefully to be avoided — ^The Preparations of Indigo for the Pastel Vat. — VI., 
Of the Woad Vat.— VII., Of the Indigo Vat.— VIII., Of the Cold Indigo Vat with Urine— A 
Hot Indigo Vat with Urine— To Reheat a Urine Vat.— IX., A Cold Indigo Vat without Urine. 
—X., Of the Method of Dyeing Blue.— XI., Of Red.— XII., Of Scarlet in Grain, or Venetian 
Scarlet.— XIII., Of Fire Scarlet.— XIV., Of Crimson.— XV., Of Gum Lac Scarlet.— XVI., Of 
the Coccus polonicus, a Colouring Insect.— XVII., Of Madder Red.— XVIII., Of Yellow.— XIX., 
Of Brown or Fawn Colour. — XX., Of Black. — XXI., Of the Colours obtained from a Mixture of 
Blue and Red.— XXII., Of the Mixture of Blue and Yellow.— XXI 1 1., Of the Mixture of Blue 
and Fawn Colour.— XXI V., Of the Mixture of Blue and Black.— XXV., Of the Mixture of Red 
and Yellow.— XXVI., Of the Mixture of Red and Fawn.— XXVII., Of the Mixture of Red and 
Black.— XXVIII., Of the Mixture of Yellow and Fawn Colours.— XXIX., Of the Mixture of 
Yellow and Black.— XXX., Of the Mixture of Fawn Colour and Black.— XXXI., Of the Prin- 
cipal Mixtures of the Primitive Colours by Three and Three.-^XXXII., The Method of Blending 
Wool of Different Colours for mixed Cloth or Stuffs.— XXXIII., The Method of Preparing 
Felts for Trial.— XXXI V., The Method of Dyeing Woollens False Colours.— XXXV., Of Flock 
or Goats' Hair.— XXXVI., Of Archil, and the Method of Using It.— XXXVII., Of Logwood.— 
XXXVIII., Of Brazil Wood.— XXXIX., Of Fustic— XL., Roucou.— XLI., Of French Berries. 
— XLI I., Of Turmeric. — XLI 1 1., Instructions for the Proof Liquor for Wool and Woollen 
Stuffs. 

Part II., The Art of Dyeing* Silk : Ungumming and Boiling for White. — For Boiling of 
Silks Intended to be Dyed. — Observations on Ungumming and Boihng. — Of White. — Of Whiten- 
ing. — Sulphuring. — Observations on Whitening and Stuphuring. — Of Aluming. — Remarks on 
Aluming. — Of Blue. — Remarks on the Blue of Indigo. — Of Yellow. — Remarks on Yellow. — 
Aurora, Orange, Mordore, Gold Colour and Chamois. — Red and Crimson. — Remarks on 
Crimson. — Of False Crimson or the Red of Brazil. — Remarks on the Red, or Crimson of Brazil 
Wood. — Of Scarlet, Orange, Red and Cherry Colour. — Preparation of the Carthamus or 
Bastard Saffron. — Remarks on the Dye of Carthamus or Bastard Saffron.— Of the False 
Poppy or Fire Colour Produced with Brazil Wood. — False Rose Colour. — Of Green. — 
Remarks.— Of Olives.— Remarks.— Of Violet.— Of Fine Violet, or Violet in Grain.— Of False 
or Common Violets or Lilac. — Of the Violet of Logwood.— Remarks. — Violet of Logwood and 
Verdigris, — Violets of Brazil and Logwood. — Remarks. — Violets from Brazil Wood and Archil. 
— Of Purple, Gillyflower, and of Fine Cochineal or Purple. — Of False Purple. — Of Maroons, 
Cinnamons and White Lees. — Remarks. — Of Nut Greys, Thorn Greys, Black and Iron Greys 
and others of the same Species. — Of Black. — Softening of Black. — Black in the Raw. — Remarks 
on Black. — Particular Process Communicated by M. Hellot.^-Genoa Crimson, a Process 
Proved in May, 1743.— Violet Crimson of Italy. — Half Violet.— Genoa Black for Velvets. 

Part III., The Art of Dyeing Cotton and Linen Thread, togrether with the Method 

of Stampin|r5ilks, Cottons, etc. : Of Dyeing in General.— Inquiry concerning Wool, Silk, 

I Cotton and Flax.— Of Wool.— Of Silk.— Of Cotton.— Of Flax.— Conclusion from the Examina- 

I 



30 

tion of Substances Commonly Dyed. — Of Bleaching. — Preparation for Stuffs to be Dyed. — 
Astringents. — Theory of Dyemg Stuffs Prepared with Alum. — Of Colouring Substances. — 
Of Cochineal and Colouring Insects. — Of Madder. — Of Vegetables Furnishing a Yellow Dye. — 
Of the Colouring Drugs Used in Dyeing without Astringents. — Of Indigo.— Of Substances 
Used in Dyeing Fawn and Root Colour. — Of Carthamus, Roucou, etc. — Of Black. Of Dyeing' 
of Cotton Thread : Of Cleansing.— Of the Colours Employed for the Dyeing of Cotton 
Thread.— Of Blue.— Of Red.— Adrianople Red.— Observations on this Dye.— Of Yellow.— Of 
Green.— Of Violet.— Of Red Cinnamon.— Of Black.— Black for Linen and Cotton Thread by a 
Combination of Colours. — Of Grey. — Of More Durable Greys. — Of Musk Colour.— Olive and 
Duck Greens. — Of Browns, Maroons, Coffee Colours, etc. — Of Silk Stuflte Dyed of Several 
Colours. — ^The Manner of Staniping Silk, etc., in Europe.— Of a Linen with a Blue Ground 
and White Pattern. — Of Saxon Blue. — Observations on this Dye. — Indexes. 

THE DYEING OF COTTON FABRICS: A Practical 

Handbook for the Dyer and Student. By Franklin Beech, Practical 
Colourist and Chemist. 272 pp. Forty-four Illustrations of Bleaching 
and Dyeing Machinery. Demy 8vo. 1901. Price 7s. 6d. ; India 
and Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 

Contents. 

Chapters I., Structure and Chemistry of the Cotton Fibre. — II., Scouring and Bleaching of 
Cotton. — III., Dyeing Machinery and Dyeing Manipulations. — IV., Principals and Practice of 
Cotton Dyeing — 1, Direct Dyeing; 2, Direct Dyeing followed by Fixation with Metallic Salts; 
3, Direct Dyeing followed by Fixation with Developers ; 4, Direct Dyeing followed by Fixation 
with Couplers ; 5, Dyeing on Tannic Mordant ; 6, Dyeing on Metallic Mordant ; 7, Production 
of Colour Direct upon Cotton Fibres; 8, Dyeing Cotton by Impregnation with Dye-stuff Solu- 
tion.— V., Dyeing Union (Mixed Cotton and Wool) Fabrics.^VI., Dyeing Half Silk (Cotton- 
Silk, Satin) Fabrics. — VII., Operations following Dyeing — Washing, Soaping, Drying. — VIII., 
Testing of the Colour of Dyed Fabrics. — IX., Experimental Dyeing and Comparative Dye 
Testing. — Index. 

The book contains numerous recipes for the production on Cotton Fabrics of all kinds of a 
great range of colours, thus making it of great service in the Dyehouse, while to the Student it 
IS of value in that the scientific principles which underlie the operations of dyeing are clearly 
laid down. 

COTTON SPINNING (First Year). By Thomas Thornley, 
Spinning Master, Bolton Technical School. 160 pp. 84 Illustrations. 
Crown 8vo. 1901. Price 3s. ; Abroad, 3s. 6d. ; strictly net. 

Contents. 

Syllabus and Examination Papers of the City and Guilds of London Institute. — Chapters 
I., Cultivation, Classification, Ginning, Baling and Mixing of the Raw Cotton. — 11., Bale- 
Breakers, Mixing Lattices and Hopper Feeders — III., Opening and Scutching. — IV., Carding. 
— Index to Illustrations. — General Index. 

COTTON SPINNING (Intermediate, or Second Year). By 
Thomas Thornley. 180 pp. 70 Illustrations. Crown 8vo. 1901. 
Price 5s. ; India and British Colonies, 5s. 6d. ; Other Countries, 6s. ; 
strictly net. 

Contents. 

Syllabuses and Examination Papers of the City and Guilds of London Institute. — Chapters 
I., The Combing Process.— II., The Drawing Frame. — III., Bobbin and Fly Frames. — IV., Mule 
Spinning. — V., Ring Spinning. — Index to Illustrations. — General Index. 

COTTON SPINNING (Honours, or Third Year). By Thomas 
Thornley. 216 pp. 74 Illustrations. Crown 8vo. 1901. Price 5s. ; 
India and British Colonies, 5s. 6d. ; Other Countries, 6s. ; strictly net. 

Contents. 

Syllabuses and Examination Papers of the City and Guilds of London Institute. — Chapters 
I., Cotton. — II., The Practical Manipulation of Cotton Spinning Machinery. — III., Doubling 
and Winding. — IV., Reeling. — V., Warping. — VI., Production and Costs. — VII., Main Driving. 
— VIII., Arrangement of Machinery and Mill Planning. — IX., Waste and Waste Spinning. — 
Index to Illustrations. — General Index. 

Books for Mining Engineers 
and Steam Users. 

RECOVERY WORK AFTER PIT FIRES. A Description 

of the Principal Methods Pursued, especially in Fiery Mines, and of 
the Various Appliances Employed, such as Respiratory and Rescue 
Apparatus, Dams, etc. By Robert Lamprbcht, Mining Engineer and 



31 

Manager. Translated from the German. Illustrated by Six large 

Plates, containing Seventy-six Illustrations. 175 pp., demy 8vo. 1901, 

Price 10s. 6d. ; India and Colonies, lis.; Other Countries, 12s.; 

strictly net. Contents. 

Preface. — I., Causes of Pit Fires: 1, Fires Resulting from the Spontaneous Ignition of 
Coal; 2, Fires Caused by Burning Timber; 3, Fires Caused by Fire-damp Explosions. — II., 
Preventive Regulations : 1, The Outbreak and Rapid Extension of a Shaft Fire can be 
most reliably prevented by Employing little or no Combustible Material in the Construction of 
the Shaft; 2, Precautions for Rapidly Localising an Outbreak of Fire in the Shaft; 3, Pre- 
cautions to be Adopted in case those under 1 and 2 Fail or Prove InefBcient Precautions 
against Spontaneous Ignition of Coal. Precautions for Preventing Explosions of Fire-damp 
and Coal Oust. Employment of Electricitv in Mining, particularly in Fiery Pits. Experiments 
on the Ignition of Fire-damp Mixtures andf Clouds of Coal Dust by Electricity. — III., indica- 
tions of an Existing or Incipient Fire.— IV., Appliances for Working in Irrespirable 
Oases : 1, Respiratory Apparatus; 2, Apparatus with Air Supply Pipes, {a) The Bremen Smoke 
Helmet, (6) The Miiller Smoke Helmet, (c) The Stolz Rescue Mask; 3, Reservoir Apparatus; 
4, Oxygen Apparatus. The Schwann Respiratory Apparatus. The Fleuss Respiratory Ap- 
paratus. The Improved Walcher-Gartner Pneumatophor, (a) The Single Bottle Apparatus, 
Instructions for Using the Pneumatophor, Taking to Pieces and Resetting the Apparatus 
ready for Use ; (6) Two Bottle Apparatus (Shamrock Type). The Neupert Rescue Apparatus 
(The Mayer-Pilar System).— V. Extinguishing Pit Fires : (a) Chemical Means; {b) Extinction 
with Water. Dragging down the Burning Masses and Packing with Clay ; (r) Insulating the 
Seat of the Fire by Dams. Dam Building. Dam Work in the Fiery Pits of Southern Hungary : 
(a) Cross-dams of Clay ; (6) Masonry Dams, Gallery Linings. Wagner's Portable Safety Dam. 
Analyses of Fire Gases. Isolating the Seat of a Fire with Dams : Working in Irrespirable 
Gases ("Gas-diving '*) : 1, Air-Lock Work (Horizontal Advance) on the Mayer System as Pur- 
sued at Karwin in 1894 ; 2, Air-Lock Work (Horizontal Advance) by the Mauerhofer Modified 
System. Vertical Advance. Mayer System. Complete Isolation of the Pit. Flooding a 
Burning Section isolated by means of Dams. Wooden Dams: (a) Upright Balk Dams; (6) 
Horizontal Balk Dams ; (c) Wedge Dams, Masonry Dams. Examples of Cylindrical and Dome- 
ihaped Dams. Dam Doors : Flooding the Whole Pit. — ^VI., Rescue Stations : {a) Stations 
above Ground; (6) Underground Rescue Stations.— VII., Spontaneous Ignition of Coal In 
Bulk. — Index. 

Illustrations. 

Sheet I., Respiratory and Rescue Appliances— Precautions against Fire. Figs. 1, 
Smoke Helmet; 2, Miiller's Smoke Helmet; 3, Low^-pressure Respiration Apparatus; 4, High- 
pressure Respiration Apparatus ; 5, The Stolz Mask for Rescue Work ; 6, Precautions against 
Fire.— Sheet II., Respiratory and Rescue Apparatus. Figs. 1, Recovery Work with 
Miiller's Smoke Helmet after a Fire ; 2-8, The Fleuss Respiration Apparatus ; 9, The Walcher- 
Gartner Pneumatophor: 10-12, Pneumatophor (Shamrock Type). — Sheet III., Respiratoiy 
and Rescue Apparatus— Stretchers. Figs. 1-8, Rescue Apparatus manufactured by C5. 
Neupert's Successor (Mayer-Pilar System) ; I, Front View ; 2, Section through Bag and Mask ; 
3, Rear View ; 4, Apparatus and Mask laid out Flat (view from above) ; 5, Apparatus and Mask 
laid out Flat (view from below) ; 6, Locking Device for Closing Bag; 7, Apparatus Complete, 
Mounted for Rescue Work; 8, Improved Valve in the Respiration Tubes; 9-12, Stretchers. 
Fig. 9, Stretcher Covered with Brown Canvas ; 10, Stretcher Covered with Brown Canvas, 
fitted with Adjustable Head-rest: 11, Folding Stretcher Covered with Brown Canvas; 12, 
Rupprecht's Stretcher Covered with Brown Canvas ; 13, Dr. Rijhlmann's Stretcher. — Sheet 
IV., Dams. Figs. 1-7, R. Wagner's Portable Safety Dam.— Sheet V., Signalling Appliances 
— Dam Construction— Cable Laying. Figs. 1-3, Signalling Appliances ; 1, Small Induction 
Apparatus for Pit Work ; 2, Bell Signal for Pit Work ; 3, Pit Telephone ; 4-18, Dam Con- 
struction; 4, 5, Upright Timber Dam; 6, 7, Timber Dam with Wooden Door; 8, 9, Dome- 
shaped Dams; 10, 11, Dome-shaped Dam with Iron Door; 12, 13, The Wenker and Berninghaus 
Locking Device for Dam Doors; 14-17, Dam Construction; 18, Damming a Gallery Lined with 
Iron ; 19, Support for Cable.— Sheet VI., Working with Diving Qear in Irrespirable Oases 
— Gallery Work. Figs. 1-4, Air-Lock Work (Mayer System); 5-7, Air-Lock (Mauerhofer's 
Modification of the Mayer System) ; 8-1 1 , Construction of Dams at the Pluto Shaft. — Sheet 
VII., Working with Diving Qear in Irrespirable Oases (Mayer System)— Appliances in 
the Shaft. Figs. 1, 2, Sections of Shaft and Air Apparatus; 3, Salzmann Reducing Valve for 
Reserve Air Supply ; 4, 5, L. v. Bremen's Respiration Apparatus with Karwin Reserve Ap- 
pliance ; 6, Cross Section of the Franziska Shaft ; 7, Method of Supplying Air to Main Pipe 
and Winding same on Drum ; 8, Clamp. 

Press Opinions. 

" A work of this extremely valuable character deserves to be made widely known amongst 
collierv managers and mining engineers at home and abroad." — Coal and Iron, 

" This book is, in a manner, unique. The literature of mining accidents is fairly extensive, 
but it consists largely of departmental Blue Books." — Sheffield Daily Telegraph. 

" A concise and lucid description of the principal methods pursued, especially in fiery 
mines, and of the various appliances employed, such as respiratory and rescue apparatus, 
dams, etc." — Staffs Advertiser, 

"The prevention of spontaneous combustion in collieries and the extinction of underground 
fires are duties that fall heavily on many colliery managers. They should, therefore, welcome 
this translation of Mr. Lamprecht's German treatise." — Ironmonger. 

** The book under notice supplies the needed full description, drawings, and mode of using 
these new appliances in actual fires, and should be studied by every colliery manager, seeing 
that even our best mana||ed collieries have not been free from fires, more or less disastrous 
to life and property. — Colliery Manager, 



32 
THE PREVENTION OF SMOKE. Combined with the 

Economical Combustion of Fuel. By W. C. Popplewell, M.Sc, 
A.M.Inst., C.E., Consulting Engineer. 46 Illustrations. 190 pp. 
1901. Demy 8vo. Price 7s. 6d. ; India and Colonies, 8s. ; Other 
Countries, 8s. 6d. ; strictly net. 

Contents. 

Introductory. — Chapters I., Fuel and Combustion. — II., Hand Firing in Boiler Furnaces. — 
III., Stoking by Mechanical Means. — IV., Powdered Fuel. — V., Gaseous Fuel. — VI., Bflficiency 
and Smoke Tests of Boilers. — VII., Some Standard Smoke Trials. — VIII., The Legal Aspect 
of the Smoke Question. — IX., The Best Means to be adopted for the Prevention of Smoke. — 
Index. 

GAS AND GOAL DUST FIRING. A Critical Review of 

the Various Appliances Patented in Germany for this purpose since 
1885. By Albert Putsch. 130 pp. Demy 8vo. 1901. Translated 
from the German. With 103 Illustrations. Price 7s. 6d. ; India and 
Colonies, 8s. ; Other Countries, 8s. 6d. ; strictly net. 

Contents. 

Generators — Generators Employing Steam — Stirring and Feed Regulating Appliances — 
Direct Generators — Burners — Regenerators and Recuperators — Glass Smelting Furnaces — 
Metallurgical Furnaces — Pottery Furnace — Coal Dust Firing. — Index. 

Press Opinions. 

"The work is worthy of perusal by all consumers of fuel. It is exceedingly well printed 
and illustrated." — Chemical Trade Journal. 

" The book will appeal with force to the manufacturer as well as to the technical student, 
whilst it is also of far more than average interest to the general reader." — Halifax Guardiati. 

"The importance that gas and coal dust firing have attained of recent years, and especially 
the great interest attaching of late to the question of coal dust firing, makes the appearance 
of the present volume most opportune." — Irori and Coal Trades Review. 

" The German author has long followed the development of various systems of gas firing, 
and in the present treatise he discusses the merits of appliances patented since 1885. His text 
and the numerous illustrations indispensable to it will be found useful by all who are engaged 
in practical work in the same field." — North British Daily Mail. 

Books on Plumbing, Decorating, 
Metal Work, etc., etc. 

EXTERNAL PLUMBING WORK. A Treatise on Lead 

Work for Roofs. By John W. Hart, R.P.C. 180 Illustrations. 270 
pp. Demy 8vo. 1896. Price 7s. 6d. ; India and Colonies, 8s. ; Other 
Countries, 8s. 6d. ; strictly net. 

Contents. 

Chapters I., Cast Sheet Lead. — II., Milled Sheet Lead. — III., Root Cesspools. — IV., Socket 
Pipes. — v., Drips. — VI., Gutters. — ^VII., Gutters (continued). — VIII., Breaks. — IX., Circular 
Breaks.— X., Flats.— XL, Flats (continued).— XII., Rolls on Flats.- XIII., Roll Ends.- XIV., 
Roll Intersections.— XV., Seam Rolls.— XVI., Seam Rolls (continued).— XVI L, Tack Fixings. 
— XVIIL, Step Flashings.— XIX., Step Flashings (continued).— XX., Secret Gutters.— X^., 
Soakers. — XXII., Hip and Valley Soakers. — XXIIL, Dormer Windows. — XXIV., Dormer 
Windows (continued).— XXV., Dormer Tops.— XXVI., Internal Dormers.— XXVI I., Skylights. 
—XXVIII., Hips and Ridging.— XXIX., Hips and Ridging (continued).— XXX., Fixings for 
Hips and Ridging.— XXXL. Ornamental Ridging.— XXXII., Ornamental Curb Rolls.— XXXI 1 1., 
Curb Rolls.— XXXIV., Cornices.— XXXV., Towers and Finials.— XXXVL, Towers and Finials 
(continued).— XXXVI I.,Towers and Finials (continued).— XXXVI 1 1., Domes.— XXXIX., Etomes 
(continued). — XL., Ornamental Lead Work. — XLL, Rain Water Heads. — XLIL, Rain Water 
Heads (continued). — XLIII., Rain Water Heads (continued). 

Press Opinions. 

" This is an eminently practical and well-illustrated volume on the management of external 
ead work." — Birmingham Daily Post. 

*' It is tfaioroughly practical, containing many valuable hints, and cannot fail to be of great 
benefit to those who have not had large experience." — Sanitary Journal. 

" Works on sanitary plumbing are by no means rare, but treatises dealing with external 
plumbing work are sumciently scarce to ensure for Mr. Hart's new publication a hearty recep- 
tion." — The Ironmonger. 

" With Mr. Hart's treatise in his hands the young plumber need not be afraid of tacklinjg 
outside work. He would do well to study its pages at leisure, so that he may be ready for it 
when called upon." — Ironmongery. 



33 

aiNTS TO PLUMBERS ON JOINT WIPING, PIPE 
BENDING AND LEAD BURNING. Third Edition, 
Revised and Corrected. By John W. Hart, R.P.C. 184 Illustrations. 
313 pp. Demy 8vo. 1901. Price 7s. 6d. ; India and Colonies, Ss. ; 
Other Countries, 8s. 6d. ; strictly net. 

Contents. 

Intrcxluction. — Chapters I., Pipe Bending. — II., Pipe Bending (continued). — III., Pipe 
Bending (continued). — IV., Square Pipe Bendings. — V., Half-circular Elbows. — VI., Curved 
Bends on Square Pipe. — VII., Bossed Bends. — VIII., Curved Plinth Bends. — IX., Rain-water 
Shoes on Square Pipe. — X., Curved and Angle Bends. — XL, Square Pipe Fixings. — XII., Joint- 
-!viping. — XIII., Substitutes for Wiped Joints. — XIV., Preparing Wiped Joints. — XV., Joint 
Fixings.— XVI., Plumbing Irons.— XVII., Joint Fixings.— XVIII., Use of "Touch" in Solder- 
intf.— OCIX., Underhand Joints. — XX., Blown and Copper Bit Joints. — XXI., Branch Joints. — 
X5CII., Branch Joints (continued). — ^XXIII., Block Joints. — XXIV., Block Joints (continued). — 
XXV., Block Fixings.— XXVI., Astragal Joints— Pipe Fixings.— XXVII., Large Branch 
Joints.— XXVII I., LanSe Underhand Joints.— XXIX., Solders.-^CXX., Autogenous Soldering 
or Lead Burning. — Index. 

Press Opinions. 

** Rich in useful diagrams as well as in hints." — Liverpool Mercury. 

" The papers are eminently practical, and go much farther into the mysteries they describe 
than the title * Hints ' properly sugf^ests." — Scotsman. 

** The articles are apparently written by a thoroughly practical man. As a practical guide 
the book vtrill doubtless oe of much service." — Glasgow Herald. 

** So far as the practical hints in this work are concerned, it will be useful to apprentices and 
students in technical schools, as it deals mainly with the most important or difficult branches 
of the plumber's craft, v(2., joint wiping, pipe bending and lead burning. . . . 'Hints' are the 
most useful things to an apprentice, and there are many in this work which are not to be found 
in some of the text-books." — English Mechanic. 

"22 Prymb Street, Hull, 24th November^ 1894. 

" Gentlemen, — ^Your books to hand for which accept my best thanks, also for circulars. I 
myself got one of J. W. Hart's books on Plumbing from your traveller, and having looked 
through the same I can safely recommend it as being the best book I have seen. Mr. J. W. 
Hart treats exhaustively upon soldering and pipe bending, which are two of the most essential 
branches in the plumbing trade.' 

THE PRINCIPLES AND PRACTICE OF DIPPING, 
BURNISHING, LACQUERING AND BRONZING 
BRASS WARE. By W. Norman Brown. 35 pp. Crown 

8vo. 1900. Price 2s. ; Abroad, 28. 6d. ; strictly net. 

Contents. 

Chapters I., Cleansing and Dipping ; Boiling up and Cleansing ; Dipping. — 11^ Scratch- 
brushing and Burnishing; Polishing; Burnishing. — III., Lacquering; "TooTs; Lacquers. — 
IV., Bronzing ; Black Bronzing ; Florentine Red Bronzing ; Green Bronzing. — Index. 

Press Opinions. 

** Mr. Brown is clearly a master of his craft, and has also the immense advantage of being 
able to convey his instructions in a manner at once clear and concise." — Leicester Post. 

**A thoroughly practical little treatise on the subject in all its branches, and one which 
should be in the hands of every tradesman or amateur who has lacquering to do." — Irish Builder. 

WORKSHOP WRINKLES for Decorators, Painters, Paper- 
hangers and Others. By W. N. Brown. Crown 8vo. 128 pp. 1901. 
Price 2s. 6d. ; Abroad, 3s. ; strictly net. 

Contents. 

Parts I., Decorating. — II., Painting. — III., Paper-hanging. — IV., Miscellaneous. 
Arranged in alphabetical order. 

HOUSE DECORATING AND PAINTING. By W. 

Norman Brown. Eighty-eight Illustrations. 150 pp. Crown Svo. 
1900. Price 3s. 6d. ; India and Colonies, 4s. ; Other Countries, 4s. 6d. . 
strictly net. Contents. 

Chapters I., Tools and Appliances. — II., Colours and Their Harmony. — III., Pigments and 
Media. — IV., Pigments and Media.— V., Pigments and Media.— VI., Pigments and Media.— 
VII., Preparation of Work, etc. — VIII., Application of Ordinary Colour. — IX., Graining. — 
X., Graining.— XI., Graining.— XII., Gilding.— XIII., Writing and Lettering.— XIV., Sign 
Painting. — ^XV., Internal Decoration. — Index. 

Press Opinion. 

"The author is evidently very thoroughly at home in regard to the technical subjects he has 
set himself to elucidate, from the mechanical rather than the artistic point of view, although 
the matter of correctness of taste is by no means ignored. Mr. Brown's style is directness 
itself, and there is no tyro in the painting trade, however mentally ungifted, who could fail to 
carry away a clearer grasp of the details of the subject after going over the performance."— 
Building Industries. 



34 
A HISTORY OP DECORATIVE ART. By W. Norman 

Brown. Thirty-nine Illustrations. 96 pp. Crown 8vo. 1900. Price 
29. 6d. ; Abroad, 3s. ; strictly net. 

Contents. 

Chapters I., Primitive and Prenistoric Art. — II., Egyptian Art. — III., Assyrian Art. — IV., 
The Art of Asia Minor.— V., Etruscan Art.— VI., Greek Art.— VII., Roman Art.— VIII., 
Byzantine Art. — IX., Lombard or Romanesque Art. — X., Gothic Art. — XL, Renaissance Art. — 
XI L, The Victorian Period. — Index. 

Press Opinion. 

" In the course of a hundred pages with some fortjr illustrations Mr. Brown gives a very 
interesting and comprehensive survey of the progress and development of decorative art. It 
cannot, of course, be pretended, that in the limited space named the subject is treated ex- 
haustively and in full detail, but it is sufficiently complete to satisfy any ordinary reader ; 
indeed, for general purposes, it is, perhaps, more acceptable than a more elaborate treatise." — 
Midland Counties Herald.' 

A HANDBOOK ON JAPANNING AND ENAMELLING 

FOR CYCLES, BEDSTEADS, TINWARE, ETC. By 

William Norman Brown. Price 2s. net. [Ready, 

Contents. 

A Pew Words on Enamelling — Appliances and Apparatus — Japans or Enamels — To Test 
Enamel for Lead — Japanning or Enamelling Metals — Japanning Tin, such as Tea Trays, and 
similar Goods — Enamelling Old Work — Enamel for Cast Iron — Enamel for Copper Cooking 
Utensils — ^The Enamelling Stove — Enamelling Bedsteads, Frames and similar large pieces — 
Paints and Varnishes for Metallic Surfaces — Varnishes for Ironwork — Blacking for Iron — 
Processes for Tin Plating — Galvanising — Metal Polishes — Colours for Polished Brass — ^A 
Golden Varnish for Metal — Painting on Zinc — Carriage Varnish — Japanese Varnish and its 
Application. — Index. 

THE PRINCIPLES OF HOT WATER SUPPLY.*^, By 

John W. Hart, R.P.C. With 129 Illustrations. 1900. 177 pp.", denay 
8vo. Price 7s. 6d. ; India and Colonies, 8s. ; Other Countries, 8s. 6d. ; 
strictly net. 

Contents. 

Chapters I., Water Circulatiou. — IL, The Tank System. — III., Pipes and Joints. — IV., The 
Cylinder System.— V., Boilers for the Cylinder System.— VI., The Cylinder System.— VII., The 
Combined Tank and Cylinder Svstem. — VI 1 1., Combined Independent and Kitchen Boiler. — 
IX., Combined Cylinder and Tank System with Duplicate Boilers. — X., Indirect Heating and 
Boiler Explosions.— XL, Pipe Boilers.— XI L, Safety Valves.— XII L, Safety Valves.— XI V., The 
American System. — XV., Heating Water by Steam. — XVI., Steam Kettles and Jets. — XVII.^ 
Heating Power of Steam. — XVI IL, Covering for Hot Water Pipes. — Index. 

Press Opinion. 

" If all plumbers were to read this book, and if they followed the instructions given, there 
would, we are sure, be fewer accidents from household boiler explosions, and many lives might 
be saved. No doubt the majority of householders know or care little about the subject, but 
any one who wishes to adopt the most up-to-date system of supplying hot water throughout 
his house will be able to do so if he reads Mr. Hart's book and follows the instruction given.. 
It is a work that all who have charge of domestic water supply should study. It is a practical 
and profitable book." — IVigan Observer. 

Brewing and Botanical. 

HOPS IN THEIR BOTANICAL, AGRICULTURAL 
AND TECHNICAL ASPECT, AND AS AN ARTICLE 
OF COMMERCE. By Emmanuel Gross, Professor at 
the Higher Agricultural College, Tetschen-Liebwerd. Translated 
from the German. Seventy-eight Illustrations. 1900. 340 pp. Demy 
8vo. Price 12s. 6d. ; India and Colonies, 13s. 6d. ; Other Countries,. 
15s. ; strictly net. 

Contents. 

PART L, HISTORY OF THE HOP. 

PART IL, THE HOP PLANT. Introductory.— 1'he Roots.— The Stem and Leaves.— 
Inflorescence and Flower : Inflorescence and Flower of the Male Hop ; Inflorescence and' 
Flower of the Female Hop. — The Fruit and its Glandular Structure : The Fruit and Seed. — 
Propagation and Selection of the Hop. — Varieties of the Hop : (a) Red Hops ; (6) Green Hops; 
(c) Pale Green Hops. — Classification according to the Period of Ripening: 1. Early August- 
Hops ; 2. Medium Early Hops ; 3. Late Hops. — Injuries to Growth : Malformations ; Diseases- 
Produced by Conditions of Soil and Climate: 1. Leaves Turning Yellow, 2. Summer or Sun- 
brand, 3. Cones Dropping Off, 4. Honey Dew, 5. Damage from Wind, Hail and Rain ; V^etable 
Enemies of the Hop : Animal Enemies of the Hop. — Beneficial Insects on Foc*} 



35 

PART III., CULTIVATION. The Requirements of the Hop in Respect of Climate, Soil 
and Situation : Climate; Soil; Situation. — Selection of Variety and Cuttings. — Planting a Hop 
Garden : Drainage ; Preparing the Ground ; Marking-out for Planting ; Plantmg ; Cultivation 
and Cropping of the Hop Garden in the First Year. — Work to be Performed Annually in the 
Hop Garden: Working the Ground; Cutting; The Non-cutting System; The Proper Per- 
formance of the Operation of Cuttina : I. Method of Cutting : Close Cutting, Ordinary Cutting, 
The Long Cut, The Topping Cut; 11. Proper Season for Cutting: Autumn Cutting, Spring 
Cutting ; Manuring ; Training the Hop Plant : Poled Gardens, Frame Training ; Principal 
Types of Frames ; Pruning, Cropping, Topping, and Leaf Stripping the Hop Plant ; Pickintf, 
Drying and Bagging. — Principal and Subsidiary Utilisation of Hops and Hop Gardens. — Lite 
of a Hop Garden ; Subsecjuent Cropping. — Cost of Production, Yield and Selling Prices. 

PART IV. — Preservation and Storage. — Physical and Chemical Structure of the Hop Cone. 
—Judging the Value of Hops. 

PART v.— Statistics of Production.— The Hop Trade.— Index. 

Press Opinions. 

" The subject is dealt with fully in every little detail ; consequently, even the veriest tyro can 
take away some useful information from its pages." — Irish Farming World. 

** Farmers are but little given to reading ; but nowadays brewers have to study their trade 
and keep abreast of its every aspect, and as far as regards our trade, to them this book 
especially appeals, and will be especially useful." — Licensed Victuallers' Gazette. 

" Like an oasis in the desert comes a volume upon the above subject, by the Professor at 
the Higher Agricultural College, Tetschen-Liebwerd, Germany, who has been fortunate 
enough to obtain an excellent translator from the German in the person of Mr. Charles 
Salter. The paucity of works upon the history and cultivation of hops is surprising con- 
sidering the scope it gives for an interesting and useful work." — Hereford Times. 

**We can safely say that this book deals more comprehensively and thoroughly with the 
subject of hops than any work previously published in this country. . . . No one interested in 
the hop industry can fail to extract a larfie amount of information from Professor Gross's 
pages, which, although primarily intended for Continental readers, yet bear very closely on 
what may be termed the cosmopolitan aspects of the science of hop production."— 5o«^^ 
Eastern Gazette. 

" This is, in our opinion, the most scholarly and exhaustive treatise on the subject of hops, 
their culture and preservation, etc., that has been published, and to the hop grower especiaJly 
will its information and recommendations prove valuable. Brewers, too, will find the chapter 
devoted to ' Judging the Value of Hops ' full of useful hints, while the whole scope and tenor of ' 
the book bear testimony to the studious and careful manner in which its contents have been 
elaborated." — Brewers' Journal. 

"Considering the extent to which this country draws its hop supplies from abroad, this 
translation of Professor Gross's volume will prove an interesting and instructive addition to 
the library of any brewer or brewers' chemist, the more so as the work of translation has been 
admirably carried out in simple and vigorous English. . . . The volume is one of a valuable 
series of special technical works for trades and professions the publishers are issuing, and is 
the first so far dealing with the brewing industry." — Burton Mail. 

" A work upon the above subject must be welcomed if for no other reason than the dearth 
of books dealing with so interesting a theme, but fortunately apart from this the book will 
afford excellent reading to all interested in hops and their culture. Professor Gross takes one 
over the whole field, by commencing with the earliest history of the plant — so far back as the 
days of ancient Greece — and from both practical, theoretical and scientific standpoints, deals 
with the cultivation, classification and formation of the hop. ... In speaking of the produc- 
tion of new varieties sound information is given, and should be of value to those who are 
always in search of improvements," — Hereford Journal. 

** This work is, without doubt, the most thorough and extensive compilation on hops ever 
yet offered to the public, and for this reason should be warmly welcomed and appreciated by 
men interested in the subject. Although primarily written for those engaged in the industry 
abroad, and mainly Continental in theory and practice, it nevertheless appeals to those con- 
nected with the hop growing and brewing business in England, not only by way of a com- 
parison, but also as an instruction. The volume is at once practical and scientific, is well 
got up, and teems with illustrations and statistics. In a word, it is a book that should find 
Its way into the hands of all who are occupied in hop production and distribution at home ; 
and it also contains valuable information and suggestions for the brewers themselves." — 



r 



Brewers* Guardian. 



Public Libraries. 



BRITISH LIBRARY YEAR BOOK, 1900-1901. A Record 

of Library Progress and Work. 54 Illustrations. Crown 8vo, 345 pp. 
1900. Edited by Thomas Greenwood. Price 3s. ; abroad, 3s. 6d. ; 
strictly net. 

Contents. 

^ Notes for Libraiy Committees. Contributed Articles : The Library Rs^e. Some Points in 
Library Planning — Mr. Burgoyne. Library Classification — Mr. Jast. Developments in Lib- 
raiy Cataloguing — Mr. Quinn. Children and Public Libraries — Mr. Ballinger. Fire Prevention 
and Insurance — Mr. Davis. The Educational Work of the Libi*ary Association— Mr. Roberts. 
The Library Assistants' Association — Mr. Chambers. British Municipal Libraries established 
under the various Public Libraries or Special Acts, and those supported out of Municipal Funds 



36 

giving particulars of Establishment, Organisation, Staff, Methods and Librarians. Table 
showing the Rate, Income, Work and Hours of the Rate-supported Libraries. Statistical 
Abstracts. British non-Municipal Libraries, Endowed, Collegiate, Proprietary and others, 
showing date of Establishment, number of Volumes, Particulars of Administration, and Lib- 
rarians. Library Associations and Kindred Societies. 

Press Opinions. 

"This is a handbook which tells the reader everything about public libraries, great and 
small, in the United Kingdom. . . . The book is decidedly one of the best arranged volumes ever 
published, and there is no doubt that the editor has been at great pains to obtain the latest 
and most accurate information from all places. County, district and parish councils^ 
ministers of religion, and schoolmasters everywhere should make themselves acquainted with 
its contents. Its perusal cannot fail to serve the ends of the library movement. The illustra- 
tions, of which there is a large number, are very good." — Western (Cardiff) Mail. 

WORKS IN PREPARATION. 
PRINCIPLES OF SIDEROLOGY (The Science of Iron). 

Translated from the German of Hanns Freiherr v. Zuptner. 

STAINED GLASS (Ancient and Modern) and FRET LEAD 
GLAZING. By E. R Suffling. 

TREATISE ON CLOTH FINISHING. By Robert 

Beaumont, of Yorkshire College, Leeds. 

INDIA-RUBBER; GUTTA PERCHA. 

EVAPORATION, CONDENSATION AND COOLING. 

Calculations of Dimensions of Apparatus. By E. Hausbrand. 
Tables. For Chemists, Chemical and Mechanical Engineers. 

THE CHEMICAL TECHNOLOGY OF TEXTILE 
FIBRES. Spinning, Washing, Bleaching, Dyeing, Printing 
and Finishing. By Dr. G. von Georgievics. [In the Press, 

WEAVING MACHINERY. Three Vols. By Harry Nisbet. 
COLOUR TERMS : THEIR PROPER USE AND 
MEANING. By David Paterson. 

LEAD AND ITS COMPOUNDS. By Thos. Lambert. 

COTTON COMBERS AND THE COMBING PROCESS. 

By Thos. Thorn ley. [/« the Press, 

TIMBER. Its Physical and Chemical Properties, Description, 
Distribution throughout the World, Forests, Preservation of Timber, 
and Applications. From the French of Paul Charpentier. 179 Illus- 
trations. About 500 pp. 

USE OP WATER IN THE INDUSTRIAL ARTS. Com- 

position — Influences — Residual Water — Purification — ^Analysis. From 
the French of H. de la Coux. 135 Illustrations. About 500 pp. 

DYERS' MATERIALS : An Introduction to the Examination, 
Evaluation and Application of the Most Important Substances Used 
in Dyeing, Printing, Bleaching and Finishing. By Paul Herrmann » 
Ph.D. Translated by Arthur C. Wright, M.A. (Oxon.), B.Sc. 
(Lond.). [In the Press, 

HANDY GUIDES TO THE CHOICE OF BOOKS. 

Vol. I. PROSE FICTION. 

Vol. II. TECHNICAL, TRADE AND COMMERCIAL 
BOOKS. 

Others to follow. [In Preparation,. 

The Publishers will advise when any of the above books are 
ready to firms sending their addresses, 

^p^ u ' '-i -^ .^ /?